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COVER PAGE Document - USD ($)	12 Months Ended
COVER PAGE Document - USD ($)	Dec. 31, 2019	Feb. 21, 2020	Jun. 30, 2019
Cover page. [Abstract]
Entity Filer Category	Large Accelerated Filer
Title of 12(b) Security	Common Stock, par value $.01 per share
Trading Symbol	WCC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	25-1723342
Document Type	10-K
Document Transition Report	false
Document Annual Report	true
Entity Address, Address Line One	225 West Station Square DriveSuite 700
Entity Address, Postal Zip Code	15219
Entity Address, City or Town	Pittsburgh,
Entity Address, State or Province	PA
Document Period End Date	Dec. 31, 2019
Entity File Number	001-14989
Entity Registrant Name	WESCO International, Inc.
City Area Code	412
Local Phone Number	454-2200
Trading Symbol	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 2,100,000,000
Entity Common Stock, Shares Outstanding		41,873,053

Document and Entity Information Document - USD ($)	12 Months Ended
Document and Entity Information Document - USD ($)	Dec. 31, 2019	Feb. 21, 2020	Jun. 30, 2019
Entity Information [Line Items]
Entity Registrant Name	WESCO International, Inc.
Entity Central Index Key	0000929008
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		41,873,053
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Public Float			$ 2,100,000,000

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 150,902	$ 96,343
Trade accounts receivable, net of allowance for doubtful accounts of $19,309 and $17,242 in 2013 and 2012, respectively	1,187,359	1,166,607
Other accounts receivable	98,029	96,984
Inventories, net	1,011,674	948,726
Income taxes receivable	16,371	24,873
Prepaid expenses and other current assets	76,076	52,107
Total current assets	2,540,411	2,385,640
Property, buildings and equipment, net	181,448	160,878
Operating Lease, Right-of-Use Asset	235,834	0
Intangible assets, net	287,275	316,016
Goodwill	1,759,040	1,722,603
Deferred income taxes	11,248	16,374
Other assets	2,379	3,525
Total assets	5,017,635	4,605,036
Current Liabilities:
Accounts payable	830,478	794,348
Accrued payroll and benefit costs	49,508	88,105
Short-term debt	26,255	30,785
Current portion of long-term debt	430	25,429
Bank overdrafts	18,021	17,818
Other current liabilities	159,367	105,461
Total current liabilities	1,084,059	1,061,946
Long-term Debt, Excluding Current Maturities	1,257,067	1,167,311
Operating Lease, Liability, Noncurrent	179,830	0
Deferred income taxes	146,617	143,967
Other noncurrent liabilities	91,391	102,086
Total liabilities	2,758,964	2,475,310
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	0	0
Additional capital	1,039,347	993,666
Retained earnings	2,530,429	2,307,462
Treasury stock, at cost	(937,157)	(758,018)
Accumulated other comprehensive income	(367,772)	(408,435)
Total WESCO International stockholders' equity	2,258,671	2,129,726
Noncontrolling interest	(6,812)	(5,584)
Total stockholders' equity	2,265,483	2,135,310
Total liabilities and stockholders' equity	5,017,635	4,605,036
Common Stock
Stockholders' Equity:
Common Stock	593	592
Common Class B
Stockholders' Equity:
Common Stock	$ 43	$ 43

CONSOLIDATED BALANCE SHEETS CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 25,400	$ 24,500
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 8,876	$ 9,243
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Treasury stock, shares outstanding	21,850,356	18,391,042
Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	210,000,000	210,000,000
Common stock, shares issued	59,308,018	59,157,696
Common stock, shares outstanding	41,797,093	45,106,085
Common Class B
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	4,339,431	4,339,431
Common stock, shares outstanding	0	0

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 8,358,917	$ 8,176,601	$ 7,679,021
Cost of goods sold (excluding depreciation and amortization below)	6,777,456	6,609,220	6,194,366
Selling, general and administrative expense	1,173,137	1,151,944	1,101,598
Depreciation and amortization	62,107	62,997	64,017
Revenue from Contract with Customer, Excluding Assessed Tax	8,358,917	8,176,601	7,679,021
Income from operations	346,217	352,440	319,040
Interest expense, net	64,156	71,415	66,600
Income before income taxes	282,061	281,025	252,440
Provision for income taxes	59,863	55,670	89,307
Net income	222,198	225,355	163,133
Net loss attributable to noncontrolling interest	(1,228)	(1,988)	(327)
Net Income attributable to WESCO International, Inc.	223,426	227,343	163,460
Comprehensive Income:
Foreign currency translation adjustment	49,306	(99,643)	85,762
Benefit plan adjustments	(8,643)	3,798	(6,381)
Comprehensive income attributable to WESCO International, Inc.	$ 264,089	$ 131,498	$ 242,841
Earnings per share :
Basic	$ 5.18	$ 4.87	$ 3.42
Diluted	$ 5.14	$ 4.82	$ 3.38
Shipping and Handling [Member]
Cost of goods sold (excluding depreciation and amortization below)	$ 71,700	$ 74,100	$ 61,800

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Additional Capital	Retained Earnings (Deficit)	Treasury Stock	Noncontrolling Interest	Accumulated Other Comprehensive Income (Loss)	Common Class B	Common Stock
Common Stock, Value, Issued							$ 43	$ 588
Common Stock, Shares, Issued							4,339,431	58,817,781
Additional Paid in Capital, Common Stock	$ 986,020
Retained Earnings (Accumulated Deficit)	1,914,757
Treasury Stock, Value	$ (542,537)
Treasury Stock, Shares	(14,545,715)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (3,269)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(391,971)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (4,583)				$ 3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				(51,401)				(243,361)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	14,809
APIC, Share-based Payment Arrangement, Recognition and Exercise	(407)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation		$ (1,304)	$ 1,480					$ 0
Treasury Stock, Value, Acquired, Par Value Method		38
Treasury Stock, Value, Acquired, Cost Method	$ (100,038)
Treasury Stock, Shares, Acquired	(1,778,537)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation								(15,380)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 327				$ 327
Translation adjustment						$ 85,762
Benefit plan adjustments	6,381					(6,381)
Net Income attributable to WESCO International, Inc.	163,460
Common Stock, Value, Issued							$ 43	$ 591
Common Stock, Shares, Issued							4,339,431	59,045,762
Additional Paid in Capital, Common Stock	999,156
Retained Earnings (Accumulated Deficit)	2,079,697
Treasury Stock, Value	$ (647,158)
Treasury Stock, Shares	(16,375,653)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (3,596)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(312,590)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (841)				$ 1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				(11,943)				(130,371)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	10,790
APIC, Share-based Payment Arrangement, Recognition and Exercise	(45)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation		(1,254)	422					$ 0
Treasury Stock, Value, Acquired, Par Value Method		(14,981)
Treasury Stock, Value, Acquired, Cost Method	$ (110,019)
Treasury Stock, Shares, Acquired	(2,003,446)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation								(18,437)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 1,988				1,988
Translation adjustment						(99,643)
Benefit plan adjustments	(3,798)					3,798
Stockholders' equity at period end at Dec. 31, 2018	2,129,726
Net Income attributable to WESCO International, Inc.	227,343
Common Stock, Value, Issued							$ 43	$ 592
Common Stock, Shares, Issued							4,339,431	59,157,696
Additional Paid in Capital, Common Stock	993,666
Retained Earnings (Accumulated Deficit)	2,307,462
Treasury Stock, Value	$ (758,018)
Treasury Stock, Shares	(18,391,042)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (5,584)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(408,435)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (238)				$ 1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				(3,730)				(198,985)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	19,062
APIC, Share-based Payment Arrangement, Recognition and Exercise	(84)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation		(2,198)	$ (459)					$ 0
Treasury Stock, Value, Acquired, Par Value Method		$ 28,901
Treasury Stock, Value, Acquired, Cost Method	$ (178,901)
Treasury Stock, Shares, Acquired	(3,455,584)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation								(48,663)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 1,228				$ 1,228
Translation adjustment						49,306
Benefit plan adjustments	8,643					$ (8,643)
Stockholders' equity at period end at Dec. 31, 2019	2,258,671
Net Income attributable to WESCO International, Inc.	223,426
Common Stock, Value, Issued							$ 43	$ 593
Common Stock, Shares, Issued							4,339,431	59,308,018
Additional Paid in Capital, Common Stock	1,039,347
Retained Earnings (Accumulated Deficit)	2,530,429
Treasury Stock, Value	$ (937,157)
Treasury Stock, Shares	(21,850,356)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (6,812)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (367,772)

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity Parenthetical [Abstract]
Share-based Payment Arrangement, Exercise of Option, Tax Benefit	$ 0	$ 0	$ 0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ (2,943)	$ 1,406	$ (2,361)

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income	$ 222,198	$ 225,355	$ 163,133
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,107	62,997	64,017
Stock-based compensation expense	19,062	16,445	14,809
Other Operating Activities, Cash Flow Statement	(11,175)	(3,652)	25
Interest related to uncertain tax positions	800	200	100
Deferred income taxes	13,205	9,137	(50,396)
Changes in assets and liabilities
Increase (Decrease) in Accounts Receivable	11,453	(22,934)	(112,977)
Inventories, net	(47,297)	(8,702)	(119,002)
Increase (Decrease) in Other Operating Assets	(28,785)	(4,239)	(2,829)
Accounts payable	(23,505)	(9,193)	(102,870)
Accrued payroll and benefit costs	(39,081)	18,777	24,679
Other current and noncurrent liabilities	(825)	(5,656)	64,793
Net cash provided by operating activities	224,367	296,721	149,122
Investing Activities:
Capital expenditures	(44,067)	(36,210)	(21,507)
Acquisition payments, net of cash acquired	(27,597)	0	0
Proceeds from sale of assets	16,795	12,461	6,766
Payments for (Proceeds from) Other Investing Activities	(5,931)	(10,393)	9,446
Net cash used in investing activities	(60,800)	(34,142)	(5,295)
Financing Activities:
Proceeds from (Repayments of) Short-term Debt	(29,780)	(1,454)	11,789
Proceeds from issuance of long-term debt	1,305,421	1,193,067	1,504,636
Repayments of long-term debt	(1,217,434)	(1,318,470)	(1,556,636)
Repurchase of common stock	(153,049)	(127,169)	(106,792)
Payment for Contingent Consideration Liability, Financing Activities	(11,401)	0	0
Increase (Decrease) in Book Overdrafts	204	(19,857)	8,199
Proceeds from (Payments for) Other Financing Activities	3,727	1,211	2,392
Net cash provided (used) by financing activities	(109,766)	(275,094)	(141,196)
Effect of exchange rate on cash and cash equivalents	758	(9,095)	5,191
Net change in cash and cash equivalents	54,559	(21,610)	7,822
Cash and cash equivalents at the beginning of period	96,343	117,953	110,131
Cash and cash equivalents at the end of period	150,902	96,343	117,953
Supplemental disclosures:
Interest Paid, Excluding Capitalized Interest, Operating Activities	65,275	64,702	63,795
Cash paid for taxes	64,531	61,983	65,117
Non-cash investing and financing activities:
Payments to Acquire Equipment on Lease	$ 1,341	$ 437	$ 552

ORGANIZATION	12 Months Ended
ORGANIZATION	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION	1. ORGANIZATION WESCO International, Inc. ("WESCO International") and its subsidiaries (collectively, “WESCO” or the "Company"), headquartered in Pittsburgh, Pennsylvania, is a full-line distributor of electrical, industrial and communications maintenance, repair and operating ("MRO") and original equipment manufacturer ("OEM") products, construction materials, and advanced supply chain management and logistics services used primarily in the industrial, construction, utility and commercial, institutional and government markets. WESCO serves approximately 70,000 active customers globally, through approximately 500 branches and 11 distribution centers located primarily in the United States, Canada and Mexico, with operations in 16 additional countries.

ACCOUNTING POLICIES	12 Months Ended
ACCOUNTING POLICIES	Dec. 31, 2019
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	2. ACCOUNTING POLICIES Basis of Consolidation The consolidated financial statements include the accounts of WESCO International and all of its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. Reclassifications The Consolidated Statements of Cash Flows for the years ended December 31, 2019, 2018 and 2017 include certain reclassifications to previously reported amounts to conform to the current period's presentation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates are based on management’s best knowledge of current events and actions WESCO may undertake in the future, actual results may ultimately differ from the estimates. Revenue Recognition WESCO’s revenue arrangements generally consist of single performance obligations to transfer a promised good or service, or a combination of goods and services. Revenue is recognized when control has transferred to the customer, which is generally when the product has shipped from a WESCO facility or directly from a supplier. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. Revenue for integrated supply services is recognized over time based on hours incurred as the transfer of control occurs as the services are being performed. WESCO generally satisfies its performance obligations within a year or less. WESCO generally does not have significant financing terms associated with its contracts; payments are normally received within 60 days. There are generally no significant costs associated with obtaining customer contracts. WESCO generally passes through warranties offered by manufacturers or suppliers to its customers. Sales taxes (and value added taxes in foreign jurisdictions) collected from customers and remitted to governmental authorities are excluded from net sales. Supplier Volume Rebates WESCO receives volume rebates from certain suppliers based on contractual arrangements with such suppliers. Volume rebates are included within other accounts receivable in the Consolidated Balance Sheets, and represent the estimated amounts due to WESCO based on forecasted purchases and the rebate provisions of the various supplier contracts. The corresponding rebate income is recorded as a reduction to cost of goods sold. Receivables under the supplier rebate program were $81.6 million at December 31, 2019 and $73.5 million at December 31, 2018. The supplier volume rebate as a percentage of net sales was 1.2% in 2019, and 1.3% in 2018 and 2017. Cash Equivalents Cash equivalents are defined as highly liquid investments with original maturities of 90 days or less when purchased. Allowance for Doubtful Accounts WESCO maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. WESCO has a systematic procedure using historical data and reasonable assumptions of collectability made at the local branch level and on a consolidated corporate basis to estimate allowances for doubtful accounts. If the financial condition of WESCO’s customers were to deteriorate, resulting in an impairment of their ability to make payments, additional allowances may be required. The allowance for doubtful accounts was $25.4 million at December 31, 2019 and $24.5 million at December 31, 2018. The total amount recorded as selling, general and administrative expense related to bad debts was $7.0 million, $10.9 million and $8.5 million for 2019, 2018 and 2017, respectively. Inventories Inventories primarily consist of merchandise purchased for resale and are stated at the lower of cost and net realizable value. Cost is determined principally under the average cost method. WESCO makes provisions for obsolete or slow-moving inventories as necessary to reflect reductions in value. WESCO writes down its inventories to net realizable value based on internal factors derived from historical analysis of actual losses. WESCO uses past data to identify items in excess of 36 months supply relative to demand or movement. WESCO then analyzes the ultimate disposition of identified excess inventories as they are sold, returned to supplier, or scrapped. This historical item-by-item analysis allows WESCO to develop an estimate of the likelihood that an item identified as being in excess supply ultimately becomes obsolete. WESCO applies the estimate to inventories currently in excess of 36 months supply, and reduces the carrying value of its inventories by the derived amount. Reserves for excess and obsolete inventories were $30.7 million and $27.6 million at December 31, 2019 and 2018, respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $10.0 million, $9.7 million and $8.8 million for 2019, 2018 and 2017, respectively. WESCO absorbs into the cost of inventories certain overhead expenses such as purchasing, receiving and storage and at December 31, 2019 and 2018, $71.2 million and $69.2 million, respectively, of these costs were included in ending inventories. Property, Buildings and Equipment Property, buildings and equipment are recorded at cost. Depreciation expense is determined using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over either their respective lease terms or their estimated lives, whichever is shorter. Estimated useful lives range from five to forty years for buildings and leasehold improvements and three to ten years for furniture, fixtures and equipment. Capitalized computer software costs are amortized using the straight-line method over the estimated useful life, typically three to five years, and are reported at the lower of unamortized cost or net realizable value. Expenditures for new facilities and improvements that extend the useful life of an asset are capitalized. Ordinary repairs and maintenance are expensed as incurred. When property is retired or otherwise disposed of, the cost and the related accumulated depreciation are removed from the accounts and any resulting gains or losses are recorded and reported as selling, general and administrative expenses. Of WESCO’s $181.4 million net book value of property, buildings and equipment as of December 31, 2019, $88.1 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 500 branches and 11 distribution centers, mitigating the risk of impairment. WESCO assesses its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of any such assets may not be fully recoverable. Changes in circumstances include technological advances, changes in the business model, capital structure, economic conditions or operating performance. The evaluation is based upon, among other things, utilization, serviceability and assumptions about the estimated future undiscounted cash flows that these assets are expected to generate. When the sum of the undiscounted cash flows is less than the carrying value of the asset or asset group, an impairment loss is recognized to the extent that carrying value exceeds fair value. Management applies its best judgment when performing these evaluations. Goodwill and Indefinite-Lived Intangible Assets Goodwill and indefinite-lived intangible assets are tested for impairment annually during the fourth quarter using information available at the end of September, or more frequently if triggering events occur, indicating that their carrying value may not be recoverable. WESCO tests for goodwill impairment on a reporting unit level and the evaluation involves comparing the fair value of each reporting unit to its carrying value. The fair values of the reporting units are determined using a combination of a discounted cash flow analysis and market multiples. Assumptions used for these fair value techniques, including expected operating margin and discount rate, are based on a combination of historical results, current forecasts, market data and recent economic events. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2019 and 2018, respectively, goodwill and indefinite-lived trademarks totaled $1.9 billion and $1.8 billion. WESCO performed its annual impairment tests of goodwill and indefinite-lived intangible assets during the fourth quarter. A possible indicator of goodwill impairment is the relationship of a company’s market capitalization to its book value. As of December 31, 2019, WESCO's market capitalization exceeded its book value and the fair values of its reporting units exceeded their carrying values. Accordingly, there were no impairment losses identified as a result of the annual test. The determination of fair value involves significant management judgment and management applies its best judgment when assessing the reasonableness of financial projections. Fair values are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill and indefinite-lived intangible impairment tests will prove to be an accurate prediction of future results. Definite Lived Intangible Assets Definite lived intangible assets are amortized over 2 to 20 years. A portion of definite lived intangible assets related to certain customer relationships are amortized using an accelerated method whereas all other definite lived intangible assets subject to amortization use a straight-line method. In either case, the amortization method reflects the pattern in which the economic benefits of the respective assets are consumed or otherwise used. Definite lived intangible assets are tested for impairment if events or circumstances occur indicating that the respective asset might be impaired. Insurance Programs WESCO uses commercial insurance for auto, workers’ compensation, casualty and health claims, and information technology as a risk-reduction strategy to minimize catastrophic losses. The Company’s strategy involves large deductible policies where WESCO must pay all costs up to the deductible amount. WESCO estimates the reserve for these programs based on historical incident rates and costs. The assumptions included in developing this accrual include the period of time between the incurrence and payment of a claim. The total liability related to insurance programs was $12.9 million and $13.1 million at December 31, 2019 and 2018, respectively. Income Taxes WESCO accounts for income taxes under the asset and liability method, which requires the recognition of deferred income taxes for events that have future tax consequences. Under this method, deferred income taxes are recognized (using enacted tax laws and rates) based on the future income tax effects of differences in the carrying amounts of assets and liabilities for financial reporting and tax purposes. The effect of a tax rate change on deferred tax assets and liabilities is recognized in income in the period of change. WESCO recognizes deferred tax assets at amounts that are expected to be realized. To make such determination, management evaluates all positive and negative evidence, including but not limited to, prior, current and future taxable income, tax planning strategies and future reversals of existing temporary differences. A valuation allowance is recognized if it is “more-likely-than-not” that some or all of a deferred tax asset will not be realized. WESCO regularly assesses the realizability of deferred tax assets. WESCO accounts for uncertainty in income taxes using a "more-likely-than-not" recognition threshold. Due to the subjectivity inherent in the evaluation of uncertain tax positions, the tax benefit ultimately recognized may materially differ from the estimate. WESCO recognizes interest and penalties related to uncertain tax benefits as part of interest expense and income tax expense, respectively. The Tax Cuts and Jobs Act of 2017 (the “TCJA”) imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax"). Except for the portion of previously taxed foreign earnings that have been repatriated, WESCO continues to assert that the remaining undistributed earnings of its foreign subsidiaries, the majority of which were subject to the transition tax, are indefinitely reinvested. WESCO believes it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without repatriating cash held by these foreign subsidiaries. Upon any future repatriation, additional tax expense or benefit may be incurred; however, management does not believe it will be material. The provisions of the TCJA also introduced U.S. taxation on certain global intangible low-taxed income ("GILTI"). WESCO has elected to account for GILTI tax as a component of income tax expense. Future adjustments (if any) resulting from additional regulatory guidance regarding the accounting for the income tax effects of TCJA will be recognized as discrete income tax expense or benefit in the period in which guidance is issued. Foreign Currency The local currency is the functional currency for the majority of WESCO’s operations outside the United States. Assets and liabilities of these operations are translated to U.S. dollars at the exchange rate in effect at the end of each period. Income statement accounts are translated at an exchange rate that approximates the average for the period. Translation adjustments arising from the use of differing exchange rates from period to period are included as a component of other comprehensive income (loss) within stockholders’ equity. Gains and losses from foreign currency transactions are included in net income for the period. Defined Benefit Pension Plan Liabilities and expenses for pension benefits are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated cash flows, the expected long-term rate of return on plan assets, and several assumptions relating to the employee workforce (salary increases, retirement age, and mortality). Fair Value of Financial Instruments The Company measures the fair value of financial assets and liabilities according to a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value and requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible at the measurement date; Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, and Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to measurements involving significant unobservable inputs (Level 3). Net Interest and Other Net interest and other includes interest expense, interest income, amortization of debt discount and debt issuance costs, the non-service cost components of net periodic benefit cost, and foreign exchange gains and losses from the remeasurement of certain financial instruments. Recently Adopted Accounting Pronouncements Effective January 1, 2019, WESCO adopted Accounting Standards Update (ASU) 2016-02, Leases, and all the related amendments (“Topic 842”), a comprehensive new standard that amended various aspects of existing accounting guidance for leases. The adoption of Topic 842 resulted in the recognition of right-of-use assets and lease liabilities for operating leases of approximately$240 million and$245 million, respectively, in the Consolidated Balance Sheet as of January 1, 2019, most of which relate to real estate. The adoption of Topic 842 did not have a material impact on the Consolidated Statements of Income and Comprehensive Income or Consolidated Statements of Cash Flows for the year ended December 31, 2019. The Company used the optional effective date transition method and therefore did not adjust the prior comparative periods presented herein. There was no cumulative-effect adjustment to beginning retained earnings as a result of using this method. In addition, the Company elected the package of practical expedients that allowed the adoption of Topic 842 without reassessing arrangements that commenced prior to the effective date. Additional qualitative and quantitative information about the Company's leases is disclosed in Note 9. Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which introduces new guidance for the accounting for credit losses on certain financial instruments. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Management has compared its current policy for estimating losses resulting from uncollectible trade accounts receivable to the requirements of the new standard. To support the new standard, management is currently identifying and implementing appropriate changes to the its business processes and controls. The new standard will be adopted in the first quarter of 2020. The adoption of this pronouncement is not expected to have an impact on WESCO's consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which amends the disclosure requirements for recurring and nonrecurring fair value measurements by removing, modifying and adding certain disclosures. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, which amends the disclosure requirements for all employers that sponsor defined benefit pension and other post retirement plans by removing and adding certain disclosures. The amendments in this ASU are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which removes certain exceptions to the general principles of Accounting Standards Codification Topic 740, Income Taxes, and simplifies other aspects of accounting for income taxes. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted in any interim or annual period, with any adjustments reflected as of the beginning of the fiscal year of adoption. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. Other pronouncements issued by the FASB or other authoritative accounting standards groups with future effective dates are either not applicable or are not expected to be significant to WESCO’s financial position, results of operations or cash flows.

REVENUE (Notes)

12 Months Ended

Dec. 31, 2019

Revenue from Contract with Customer [Abstract]

Revenue from Contract with Customer [Policy Text Block]

3. REVENUE

WESCO distributes products and provides services to customers globally within the following end markets: (1) industrial, (2) construction, (3) utility, and (4) commercial, institutional and government. Revenue is measured as the amount of consideration WESCO expects to receive in exchange for transferring goods or providing services.

The following tables disaggregate WESCO’s net sales by end market and geography:



	Year Ended December 31,
(In thousands)	2019		2018		2017
Industrial	$	3,000,253	$	2,983,062	$	2,852,357
Construction	2,743,852		2,684,844		2,546,261
Utility	1,347,448		1,303,697		1,181,704
Commercial, Institutional and Government	1,267,364		1,204,998		1,098,699
Total by end market	$	8,358,917	$	8,176,601	$	7,679,021



	Year Ended December 31,
(In thousands)	2019		2018		2017
United States	$	6,234,119	$	6,089,130	$	5,775,988
Canada ⁽¹⁾	1,647,066		1,647,933		1,521,378
Other International ⁽¹⁾	477,732		439,538		381,655
Total by geography	$	8,358,917	$	8,176,601	$	7,679,021


⁽¹⁾	The prior periods has been reclassified to confirm to the current period's presentation.

In accordance with certain contractual arrangements, WESCO receives payment from its customers in advance and recognizes such payment as deferred revenue. Revenue for advance payment is recognized when the performance obligation has been satisfied and control has transferred to the customer, which is generally upon shipment. Deferred revenue is usually recognized within a year or less from the date of the customer’s advance payment. At December 31, 2019 and 2018, $12.3 million and $11.8 million, respectively, of deferred revenue was recorded as a component of other current liabilities in the Consolidated Balance Sheets.

WESCO’s revenues are adjusted for variable consideration, which includes customer volume rebates, returns, and discounts. WESCO measures variable consideration by estimating expected outcomes using analysis and inputs based upon historical data, as well as current and forecasted information. Variable consideration is reviewed by management on a monthly basis and revenue is adjusted accordingly. Variable consideration reduced revenue for the years ended December 31, 2019, 2018 and 2017 by approximately $106.6 million, $107.4 million and $91.1 million, respectively.

Shipping and handling costs are recognized in net sales when they are billed to the customer. These costs are recognized as a component of selling, general and administrative expenses when WESCO does not bill the customer. WESCO has elected to recognize shipping and handling costs as a fulfillment cost. Shipping and handling costs recorded as a component of selling, general and administrative expenses totaled $71.7 million, $74.1 million and $61.8 million for the years ended December 31, 2019, 2018 and 2017, respectively.

FAIR VALUE (Notes)	12 Months Ended
FAIR VALUE (Notes)	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	4. FAIR VALUE OF FINANCIAL INSTRUMENTS The Company’s financial instruments consist of cash and cash equivalents, accounts receivable, accounts payable, bank overdrafts, and outstanding indebtedness. The Company uses a market approach to determine the fair value of its debt instruments, utilizing quoted prices in active markets, interest rates and other relevant information generated by market transactions involving similar instruments. Therefore, the inputs used to measure the fair value of the Company's debt instruments are classified as Level 2 within the fair value hierarchy. The reported carrying amounts of WESCO's financial instruments approximated their fair values as of December 31, 2019 and 2018.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

GOODWILL AND INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL AND INTANGIBLE ASSETS

. GOODWILL AND INTANGIBLE ASSETS

Goodwill

The following table sets forth the changes in the carrying value of goodwill:



	Year Ended December 31,
	2019		2018
	(In thousands)
Beginning balance January 1	$	1,722,603	$	1,771,877
Foreign currency exchange rate changes	30,670		(49,274		)
Adjustments to goodwill for acquisitions	5,767		—
Ending balance December 31	$	1,759,040	$	1,722,603

Intangible Assets

The components of intangible assets are as follows:



		December 31, 2019							December 31, 2018
	Life	Gross Carrying Amount ⁽¹⁾		Accumulated Amortization ⁽¹⁾			Net Carrying Amount		Gross Carrying Amount ⁽¹⁾		Accumulated Amortization ⁽¹⁾			Net Carrying Amount
		(In thousands)
Intangible assets:
Trademarks	Indefinite	$	98,699	$	—		$	98,699	$	96,260	$	—		$	96,260
Trademarks	10-15	24,800		(9,319		)	15,481		25,185		(7,585		)	17,600
Non-compete agreements	5	196		(180		)	16		196		(141		)	55
Customer relationships	10-20	358,341		(201,962		)	156,379		358,620		(180,395		)	178,225
Distribution agreements	10-19	37,371		(25,294		)	12,077		36,984		(22,562		)	14,422
Patents	10	48,310		(43,687		)	4,623		48,310		(38,856		)	9,454
		$	567,717	$	(280,442	)	$	287,275	$	565,555	$	(249,539	)	$	316,016


⁽¹⁾	Excludes the original cost and related accumulated amortization of fully-amortized intangible assets.

Amortization expense related to intangible assets totaled $35.5 million, $35.9 million and $37.8 million for the years ended December 31, 2019, 2018 and 2017, respectively.

The following table sets forth the estimated amortization expense for intangible assets for the next five years and thereafter:



For the year ending December 31,	(In thousands)
2020	$	34,037
2021	26,387
2022	23,903
2023	23,311
2024	19,863
Thereafter	61,075

CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS	12 Months Ended
CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS	Dec. 31, 2019
Risks and Uncertainties [Abstract]
CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS	6. CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS WESCO distributes its products and services and extends credit to a large number of customers in the industrial, construction, utility, and commercial, institutional and government markets. Based upon WESCO’s broad customer base, Managment has concluded that it has no material credit risk as a result of customer concentration. WESCO is subject to supplier concentration risk as Eaton Corporation, the Company's largest supplier, accounted for approximately 11% of its purchases in 2019, 2018 and 2017.

ACQUISITIONS

12 Months Ended

Dec. 31, 2019

Business Combinations [Abstract]

ACQUISITIONS

7. ACQUISITIONS

The following table sets forth the consideration paid for acquisitions:



	Year Ended December 31,
	2019
	(In thousands)
Fair value of assets acquired	$	35,671
Fair value of liabilities assumed	8,074
Cash paid for acquisitions	$	27,597

Sylvania Lighting Services Corp.

On March 5, 2019, WESCO Distribution, Inc. ("WESCO Distribution"), through its WESCO Services, LLC subsidiary, acquired certain assets and assumed certain liabilities of Sylvania Lighting Services Corp. ("SLS"). Headquartered in Wilmington, Massachusetts, SLS offers a full spectrum of energy-efficient lighting upgrade, retrofit, and renovation solutions with annual sales of approximately $100 million and approximately 220 employees across the U.S. and Canada. WESCO Distribution funded the purchase price paid at closing with borrowings under its accounts receivable securitization facility. The purchase price was allocated to the respective assets and liabilities based upon their estimated fair values as of the acquisition date, resulting in goodwill of $5.8 million, which is deductible for tax purposes.

PROPERTY, BUILDINGS AND EQUIPMENT

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

PROPERTY, BUILDINGS AND EQUIPMENT

8. PROPERTY, BUILDINGS AND EQUIPMENT

The following table sets forth the components of property, buildings and equipment:



	As of December 31,
	2019			2018
	(In thousands)
Buildings and leasehold improvements	$	110,056		$	111,510
Furniture, fixtures and equipment	162,029			186,523
Software costs	127,919			115,631
	400,004			413,664
Accumulated depreciation and amortization	(268,415		)	(291,811		)
	131,589			121,853
Land	24,106			23,996
Construction in progress	25,753			15,029
	$	181,448		$	160,878

Depreciation expense was $15.9 million, $17.3 million and $16.3 million, and capitalized software amortization was $10.6 million, $9.8 million and $9.9 million, in 2019, 2018 and 2017, respectively. The unamortized software cost was $29.8 million and $24.2 million as of December 31, 2019 and 2018, respectively. Furniture, fixtures and equipment include finance leases of $9.7 million and $9.3 million and related accumulated amortization of $8.3 million and $8.4 million as of December 31, 2019 and 2018, respectively.

LEASES (Notes)

12 Months Ended

Dec. 31, 2019

Lease, Cost [Abstract]

Leases of Lessee Disclosure [Text Block]

9. LEASES

WESCO leases real estate, automobiles, trucks and other equipment. The determination of whether an arrangement is, or contains, a lease is performed at the inception of the arrangement. Classification and initial measurement of the right-of-use asset and lease liability are determined at the lease commencement date. The Company elected the short-term lease measurement and recognition exemption; therefore, leases with an initial term of 12 months or less are not recorded on the balance sheet.

The Company's arrangements include certain non-lease components such as common area and other maintenance for leased real estate, as well as mileage, fuel and maintenance costs related to leased automobiles and trucks. WESCO accounts for these nonlease components separately from the associated lease components. The Company does not guarantee any residual value in its lease agreements, and there are no material restrictions or covenants imposed by lease arrangements. Real estate leases typically include one or more options to extend the lease. The Company regularly evaluates the renewal options, and when they are reasonably certain of exercise, the Company includes the renewal period in its lease term. The Company uses the interest rate implicit in its leases to discount lease payments at the lease commencement date. When the implicit rate is not readily available, the Company uses its incremental borrowing rate.

The Company's finance leases, which are recorded in the Condensed Consolidated Balance Sheet as of December 31, 2019 as a component of property, buildings and equipment, current portion of long-term debt and long-term debt, are not material to the consolidated financial statements and notes thereto. Accordingly, finance leases have not been disclosed herein.

The following table sets forth supplemental balance sheet information related to operating leases for the period presented:



	As of
(In thousands)	December 31, 2019
Operating lease assets	$	235,834

Current operating lease liabilities	62,046
Noncurrent operating lease liabilities	179,830
Total operating lease liabilities	$	241,876

The following table sets forth the Company's total lease cost, which is recorded as a component of selling, general and administrative expenses, for the period ending:



(In thousands)	December 31, 2019
Operating lease cost	$	73,613
Short-term lease cost	90
Variable lease cost	23,385
Total lease cost	$	97,088

Variable lease cost consists of the non-lease components described above, as well as taxes and insurance for WESCO's leased real estate.

The following table sets forth supplemental cash flow information related to operating leases for the period ending:



(In thousands)	December 31, 2019
Operating cash flows from operating leases	$	75,775
Right-of-use assets obtained in exchange for new operating lease liabilities	60,586

As of December 31, 2019, the weighted-average remaining lease term for operating leases was 5.3 years and the weighted-average discount rate used to measure operating lease assets and liabilities was 4.6%.

The following table sets forth the maturities of the Company's operating lease liabilities and reconciles the respective undiscounted payments to the operating lease liabilities in the Condensed Consolidated Balance Sheet as of December 31, 2019:



	(In thousands)
2020	$	72,946
2021	62,549
2022	48,490
2023	38,209
2024	22,426
Thereafter	32,559
Total undiscounted operating lease payments	277,179
Less: interest	(35,303		)
Total operating lease liabilities	$	241,876

The following table sets forth the future minimum rental payments for operating leases accounted for in accordance with Accounting Standards Codification Topic 840, Leases, as of December 31, 2018:



Years ending December 31	(In thousands)
2019	$	71,640
2020	59,594
2021	47,264
2022	34,490
2023	24,493
Thereafter	40,302

DEBT

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

DEBT

. DEBT

The following table sets forth WESCO’s outstanding indebtedness:



	As of December 31,
	2019			2018
	(In thousands)
International lines of credit	$	26,255		$	30,785
Term Loan Facility, less debt discount of $156 in 2018	—			24,594
Accounts Receivable Securitization Facility	415,000			275,000
Revolving Credit Facility	—			51,598
5.375% Senior Notes due 2021	500,000			500,000
5.375% Senior Notes due 2024	350,000			350,000
Capital leases	1,373			1,123
Total debt	1,292,628			1,233,100
Less unamortized debt issuance costs	(8,876		)	(9,575		)
Less short-term debt and current portion of long-term debt	(26,685		)	(56,214		)
Total long-term debt	$	1,257,067		$	1,167,311

International Lines of Credit

Certain foreign subsidiaries of WESCO have entered into uncommitted lines of credit, some of which are overdraft facilities, to support local operations. The maximum borrowing limit varies by facility and ranges between $2.0 million and $21.0 million. The applicable interest rate for borrowings under these lines of credit varies by country and is governed by the applicable loan agreement. The international lines of credit are renewable on an annual basis and certain facilities are fully and unconditionally guaranteed by WESCO Distribution. Accordingly, borrowings under these lines directly reduce availability under the Revolving Credit Facility. The average interest rate for these facilities was 6.32% and 8.78% at December 31, 2019 and 2018, respectively.

Term Loan Facility

On December 12, 2012, WESCO Distribution, as U.S. borrower, WDCC Enterprises Inc. ("WDCC" and together with WESCO Distribution, the “Borrowers”), as Canadian borrower, and WESCO International entered into a Term Loan Agreement (the “Term Loan Agreement”) among WESCO Distribution, WDCC, the Company, the lenders party thereto and Credit Suisse AG Cayman Islands Branch, as administrative agent and as collateral agent.

The Term Loan Agreement provided a seven-year term loan facility (the “Term Loan Facility”), which consisted of two separate sub-facilities: (i) a Canadian sub-facility in an aggregate principal amount of CAD150 million, issued at a 2.0% discount, and (ii) a U.S. sub-facility in an aggregate principal amount of $700 million, issued at a 1.0% discount. The proceeds of the Term Loan Facility were used to finance the acquisition of EECOL, and to pay fees and expenses incurred in connection with the acquisition and certain other transactions. Subject to the terms of the Term Loan Agreement, the Borrowers could request incremental term loans from time to time in an aggregate principal amount not to exceed at any time $300 million, with an equivalent principal amount in U.S. dollars being calculated for any incremental term loan denominated in Canadian dollars.

On November 19, 2013, the Borrowers and WESCO International entered into an amendment (the “Term Loan Amendment”) to the Term Loan Agreement. The Term Loan Amendment, among other things, reduced the applicable margin on U.S. term loans by 0.50% and the LIBOR floor applicable to the U.S. sub-facility from 1.00% to 0.75%. The modified pricing terms were effective December 13, 2013.

On November 26, 2013, WESCO Distribution sold $500 million aggregate principal amount of 5.375% Senior Notes due 2021 (the “2021 Notes”), and used the net proceeds plus excess cash to prepay $500 million under the Company's U.S. sub-facility of the Term Loan Facility (see discussion below under “5.375% Senior Notes due 2021” for additional information). The prepayment satisfied all remaining quarterly repayment obligations under the U.S. sub-facility. The Canadian sub-facility was fully repaid in 2015 and the remaining amount outstanding under the U.S. sub-facility was fully repaid in the first quarter of 2019.

Accounts Receivable Securitization Facility

On September 26, 2019, WESCO Distribution amended its accounts receivable securitization facility (the “Receivables Facility”) pursuant to the terms and conditions of a Ninth Amendment to the Fourth Amended and Restated Receivables Purchase Agreement, dated as of September 26, 2019 (the “Receivables Amendment”), by and among WESCO Receivables Corp. (“WESCO Receivables”), WESCO Distribution, the various purchaser groups from time to time party thereto and PNC Bank, National Association, as Administrator. The Receivables Amendment amended the amended and restated receivables purchase agreement entered into on September 24, 2015 (the “Existing Receivables Purchase Agreement” and as amended by the Receivables Amendment, the “Receivables Purchase Agreement”).

The Receivables Amendment increased the purchase limit under the Existing Receivables Purchase Agreement from $550 million to $600 million, with the opportunity to exercise an accordion feature that permits increases in the purchase limit of up to $200 million, extended the term of the Receivables Facility to September 26, 2022 and added and amended certain defined terms. The interest rate spread and commitment fee of the Receivables Facility is 0.95% and 0.45%, respectively.

Under the Receivables Facility, WESCO sells, on a continuous basis, an undivided interest in all domestic accounts receivable to WESCO Receivables, a wholly owned special purpose entity (the “SPE”). The SPE sells, without recourse, a senior undivided interest in the receivables to financial institutions for cash while maintaining a subordinated undivided interest in the receivables, in the form of overcollateralization. Since WESCO maintains control of the transferred receivables, the transfers do not qualify for “sale” treatment. As a result, the transferred receivables remain on the balance sheet, and WESCO recognizes the related secured borrowing. WESCO has agreed to continue servicing the sold receivables for the third-party conduits and financial institutions at market rates; accordingly, no servicing asset or liability has been recorded.

As of December 31, 2019 and 2018, accounts receivable eligible for securitization totaled $809.5 million and $758.3 million, respectively. The Consolidated Balance Sheets as of December 31, 2019 and 2018 include $415.0 million and $275.0 million, respectively, of account receivable balances legally sold to third parties, as well as borrowings for equal amounts. At December 31, 2019, the interest rate for this facility was approximately 2.0%.

Revolving Credit Facility

On September 26, 2019, WESCO International, WESCO Distribution and certain other subsidiaries of the Company entered into a $600 million revolving credit facility (the “Revolving Credit Facility”) as a replacement of its existing revolving credit facility entered into on September 24, 2015. The Revolving Credit Facility contains a letter of credit sub-facility of up to $125 million, pursuant to the terms and conditions of a Third Amended and Restated Credit Agreement, dated as of September 26, 2019 (the “Credit Agreement”). The Revolving Credit Facility contains an accordion feature allowing WESCO Distribution to request increases to the borrowing commitments under the Revolving Credit Facility of up to $200 million in the aggregate, subject to customary conditions.

The Revolving Credit Facility matures in September 2024 and is collateralized by (i) substantially all assets of WESCO Distribution and its subsidiaries which are party to the Credit Agreement, other than, among other things, real property and accounts receivable sold or intended to be sold pursuant to WESCO Distribution’s Receivables Facility, and (ii) substantially all assets of WESCO Canada and the other Canadian Borrowers, other than, among other things, real property, in each case, subject to customary exceptions and limitations. The obligations of WESCO Distribution and the other U.S. Borrowers under the Revolving Credit Facility have been guaranteed by the Company and certain of WESCO Distribution’s subsidiaries. The obligations of WESCO Canada and the other Canadian Borrowers under the Revolving Credit Facility have been guaranteed by certain subsidiaries of WESCO Canada and the other Canadian Borrowers. The applicable interest rate for borrowings under the Revolving Credit Facility includes interest rate spreads based on available borrowing capacity that range between 1.25% and 1.50% for LIBOR-based borrowings and 0.25% and 0.50% for prime rate-based borrowings. At December 31, 2019, the interest rate for this facility was approximately1.6%.

The Credit Agreement requires compliance with conditions precedent that must be satisfied prior to any borrowing as well as ongoing compliance with certain customary affirmative and negative covenants. The Credit Agreement contains customary events of default.

During 2019, WESCO borrowed $715.4 million under the Revolving Credit Facility and made repayments in the aggregate amount of $767.4 million. During 2018, aggregate borrowings and repayments were $473.1 million and $433.5 million, respectively. WESCO had $563.8 million available under the Revolving Credit facility at December 31, 2019, after giving effect to $28.4 million of outstanding letters of credit, $36.1 million of surety bonds, and $7.8 million of other reserves, as compared to $515.9 million available under the Revolving Credit facility at December 31, 2018, after giving effect to $27.2 million of outstanding letters of credit, $19.5 million of surety bonds, and $5.3 million of other reserves.

5.375% Senior Notes due 2021

In November 2013, WESCO Distribution issued $500 million aggregate principal amount of 2021 Notes through a private offering exempt from the registration requirements of the Securities Act of 1933, as amended (the “Securities Act”). The 2021 Notes were issued at 100% of par and are governed by an indenture (the “2021 Indenture”) entered into on November 26, 2013 between WESCO International and U.S. Bank National Association, as trustee. The 2021 Notes are unsecured senior obligations of WESCO Distribution and are guaranteed on a senior unsecured basis by WESCO International. The 2021 Notes bear interest at a stated rate of 5.375%, payable semi-annually in arrears on June 15 and December 15 of each year. In addition, WESCO incurred costs related to the issuance of the 2021 Notes totaling $8.4 million, which were recorded as a reduction to the carrying value of the debt and are being amortized over the life of the notes. The 2021 Notes mature on December 15, 2021. The net proceeds of the 2021 Notes were used to prepay a portion of the U.S. sub-facility of the term loan due 2019.

Under the terms of a registration rights agreement dated as of November 26, 2013 among WESCO Distribution, WESCO International and Merrill Lynch, Pierce, Fenner & Smith Incorporated, as the representative of the initial purchasers of the 2021 Notes, WESCO Distribution and WESCO International agreed to register under the Securities Act notes having terms identical in all material respects to the 2021 Notes (the “2021 Exchange Notes”) and to make an offer to exchange the 2021 Exchange Notes for the 2021 Notes. WESCO Distribution launched the exchange offer on June 12, 2014 and the exchange offer expired on July 17, 2014.

At any time WESCO Distribution may redeem all or a part of the 2021 Notes. On and after December 15, 2019, WESCO Distribution may redeem all or a part of the 2021 Notes at a redemption price equal to 100% of the principal amount.

The 2021 Indenture contains customary covenants and customary events of default. In addition, upon a change of control, the holders of 2021 Notes have the right to require WESCO Distribution to repurchase all or any part of the 2021 Notes at a redemption price equal to 101% of the principal amount, plus accrued and unpaid interest.

5.375% Senior Notes due 2024

In June 2016, WESCO Distribution issued $350 million aggregate principal amount of 5.375% Senior Notes due 2024 (the "2024 Notes") through a private offering exempt from the registration requirements of the Securities Act. The 2024 Notes were issued at 100% of par and are governed by an indenture (the “2024 Indenture”) entered into on June 15, 2016 among WESCO Distribution, as issuer, WESCO International, as parent guarantor, and U.S. Bank National Association, as trustee. The 2024 Notes are unsecured senior obligations of WESCO Distribution and are guaranteed on a senior unsecured basis by WESCO International. The 2024 Notes bear interest at a rate of 5.375% per annum, payable semi-annually in arrears on June 15 and December 15 of each year. WESCO incurred costs totaling $6.0 million to issue the 2024 Notes, which were recorded as a reduction to the carrying value of the debt and are being amortized over the life of the note. The notes mature on June 15, 2024. The Company used the net proceeds to redeem its 6.0% Convertible Senior Debentures due 2029 on September 15, 2016.

Under the terms of a registration rights agreement dated as of June 15, 2016 among WESCO Distribution, as the issuer, WESCO International, as parent guarantor, and Goldman, Sachs & Co., as representative of the initial purchasers of the 2024 Notes, WESCO Distribution and WESCO International agreed to register under the Securities Act notes having terms identical in all material respects to the 2024 Notes (the “2024 Exchange Notes”) and to make an offer to exchange the 2024 Exchange Notes for the 2024 Notes. WESCO Distribution launched the exchange offer on December 28, 2016 and the exchange offer expired on January 31, 2017.

At any time on or after June 15, 2019, WESCO Distribution may redeem all or a part of the 2024 Notes. Between June 15, 2019 and June 14, 2020, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 104.031% of the principal amount. Between June 15, 2020 and June 14, 2021, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 102.688% of the principal amount. Between June 15, 2021 and June 14, 2022, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 101.344% of the principal amount. On and after June 15, 2022, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 100% of the principal amount.

The 2024 Indenture contains customary covenants and events of default. Upon a change of control, the holders of the 2024 Notes have the right to require WESCO Distribution to repurchase all or any part of the 2024 Notes at a redemption price equal to 101% of the principal amount thereof, plus accrued and unpaid interest.

Debt Issuance Costs

WESCO capitalizes costs associated with the issuance of debt and such costs are amortized over the term of the respective debt instrument on a straight-line basis. Debt issuance costs are presented in the Consolidated Balance Sheets as a direct reduction from the carrying amount of the related debt liability. Upon prepayment of debt, the Company accelerates the recognition of an appropriate amount of the costs as refinancing or extinguishment of debt. As of December 31, 2019 and 2018, unamortized debt issuance costs of $8.9 million and $9.6 million were recorded in the Consolidated Balance Sheets, respectively.

Covenant Compliance

WESCO was in compliance with all relevant covenants contained in its debt agreements as of December 31, 2019.

The following table sets forth the aggregate principal repayment requirements for all indebtedness for the next five years and thereafter, as of December 31, 2019:



	(In thousands)
2020	$	26,685
2021	500,943
2022	415,000
2023	—
2024	350,000
Thereafter	—
Total payments on debt	$	1,292,628

WESCO’s credit agreements contain various restrictive covenants that, among other things, impose limitations on: (i) dividend payments or certain other restricted payments or investments; (ii) the incurrence of additional indebtedness and guarantees; (iii) creation of liens; (iv) mergers, consolidation or sales of substantially all of WESCO’s assets; (v) certain transactions among affiliates; (vi) payments by certain subsidiaries to WESCO, and (vii) capital expenditures. In addition, the Revolving Credit Facility and the Receivables Facility require WESCO to meet certain fixed charge coverage tests depending on availability or liquidity, respectively.

CAPITAL STOCK	12 Months Ended
CAPITAL STOCK	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
CAPITAL STOCK	. CAPITAL STOCK Preferred Stock There are 20 million shares of preferred stock authorized at a par value of $0.01 per share; there are no shares issued or outstanding. The Board of Directors has the authority, without further action by the stockholders, to issue all authorized preferred shares in one or more series and to fix the number of shares, designations, voting powers, preferences, optional and other special rights and the restrictions or qualifications thereof. The rights, preferences, privileges and powers of each series of preferred stock may differ with respect to dividend rates, liquidation values, voting rights, conversion rights, redemption provisions and other matters. Common Stock There are 210 million shares of common stock and 20 million shares of Class B common stock authorized at a par value of $0.01 per share. The Class B common stock is identical to the common stock, except for voting and conversion rights. The holders of Class B common stock have no voting rights. With certain exceptions, Class B common stock may be converted, at the option of the holder, into the same number of shares of common stock. The terms of the Revolving Credit Facility, as well as the indentures governing the 2021 Notes and 2024 Notes, place certain limits on the Company's ability to declare or pay dividends and repurchase common stock. The share repurchases in 2019, 2018 and 2017, as described in Note 13, were made within the limits of WESCO's various credit agreements. At December 31, 2019 and 2018, no dividends had been declared and, therefore, no retained earnings were reserved for dividend payments. Treasury Stock Common stock purchased for treasury is recorded at cost. At the date of subsequent reissue, the treasury stock account is reduced by the cost of such stock, with cost determined on a weighted-average basis.

INCOME TAXES

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

INCOME TAXES

. INCOME TAXES

The Tax Cuts and Jobs Act of 2017 (the "TCJA”), enacted on December 22, 2017, made significant changes to U.S. corporate tax law, including with respect to the U.S. corporate income tax rate, new business-related exclusions, deductions and credits, as well as international tax provisions. Most notably, the TCJA permanently reduced the U.S. corporate income tax rate from 35% to 21%, effective January 1, 2018, and imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax"). The TCJA also introduced anti-base erosion provisions, including the global intangible low-taxed income tax.

As a result of the reduction in the U.S. corporate income tax rate, the Company remeasured its U.S. deferred income tax balances and recorded a provisional deferred income tax benefit of $56.4 million for the year ended December 31, 2017. The Company also recognized provisional current income tax expense for the transition tax under the TCJA of $82.8 million for the year ended December 31, 2017. After the utilization of foreign tax credit carryforwards of $17.8 million, a provisional liability of $65.0 million was accrued for the transition tax as of December 31, 2017, which is payable over a period of eight years.

During the year ended December 31, 2018, the Company completed its accounting for the income tax effects of the TCJA, which resulted in an additional deferred income tax benefit of $0.9 million and a discrete benefit of $3.4 million. During the year ended December 31, 2019, the Company further adjusted its transition tax liability based upon guidance issued by the Internal Revenue Service ("IRS"), which resulted in a discrete benefit of $3.7 million. As of December 31, 2019 and 2018, a liability of $36.8 million and $43.2 million, respectively, was recorded as components of other current and noncurrent liabilities in the Consolidated Balance Sheets for transition tax. The transition tax will be paid in installments.

The accounting for the income tax effects of the TCJA has been completed based on regulatory guidance issued to date. Additional guidance could be issued, which could affect the amounts described above. The Company will continue to evaluate its tax positions with respect to the TCJA as the IRS releases additional regulatory guidance. Future adjustments, if any, for tax positions taken to date will be recognized as discrete income tax expense or benefit in the period in which such guidance is issued.

The following table sets forth the components of income before income taxes by jurisdiction:



	Year Ended December 31,
	2019		2018		2017
			(In thousands)
United States	$	198,566	$	198,556	$	180,957
Foreign	83,495		82,469		71,483
Income before income taxes	$	282,061	$	281,025	$	252,440

The following table sets forth the components of the provision (benefit) for income taxes:



	Year Ended December 31,
	2019		2018		2017
			(In thousands)
Current income taxes:
Federal	$	31,695	$	28,464	$	122,170
State	8,616		7,458		2,259
Foreign	6,347		10,611		15,274
Total current income taxes	46,658		46,533		139,703
Deferred income taxes:
Federal	6,774		5,253		(48,060		)
State	1,846		1,967		4,508
Foreign	4,585		1,917		(6,844		)
Total deferred income taxes	13,205		9,137		(50,396		)
Provision for income taxes	$	59,863	$	55,670	$	89,307

The following table sets forth the reconciliation between the federal statutory income tax rate and the effective tax rate:



	Year Ended December 31,
	2019		2018		2017
Federal statutory rate	21.0	%	21.0	%	35.0	%
State income taxes, net of federal income tax benefit	3.1		2.8		1.4
Deemed repatriation of undistributed foreign earnings	(1.3	)	(1.2	)	32.8
Deferred income tax remeasurement	—		(0.3	)	(22.4	)
Tax effect of intercompany financing	(5.5	)	(5.6	)	(10.5	)
Other	3.9		3.1		(0.9	)
Effective tax rate	21.2	%	19.8	%	35.4	%

As a result of the TCJA, WESCO reevaluated its intent and ability to repatriate foreign earnings based upon the liquidity of the Company's domestic operations and cash flow needs of its foreign subsidiaries. Consequently, during the years ended December 31, 2019 and 2018, WESCO repatriated a portion of the previously taxed earnings attributable to its foreign operations. WESCO continues to assert that the remaining undistributed earnings of its foreign subsidiaries, the majority of which were subject to the transition tax described above, are indefinitely reinvested. WESCO believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without repatriating cash held by these foreign subsidiaries. Upon any future repatriation, additional tax expense or benefit may be incurred; however, we do not believe such amount would be material.

The following table sets forth deferred tax assets and liabilities:



	As of December 31,
	2019					2018
				(In thousands)
	Assets			Liabilities		Assets			Liabilities
Accounts receivable	$	3,382		$	—	$	3,657		$	—
Inventories	—			4,580		—			3,315
Depreciation of property, buildings and equipment	—			18,393		—			17,384
Operating leases	61,326			60,670		—			—
Amortization of intangible assets	—			159,573		—			158,795
Employee benefits	20,641			—		20,107			—
Stock-based compensation	13,792			—		12,840			—
Tax loss carryforwards	10,486			—		15,557			—
Foreign tax credit carryforwards	1,247			—		—			—
Other	6,791			3,964		7,927			4,115
Deferred income taxes before valuation allowance	117,665			247,180		60,088			183,609
Valuation allowance	(5,854		)	—		(4,072		)	—
Total deferred income taxes	$	111,811		$	247,180	$	56,016		$	183,609

As of December 31, 2018, WESCO had a deferred tax asset of $6.4 million related to Canadian net operating loss carryforwards. These carryforwards were fully utilized during the year ended December 31, 2019. Additionally, WESCO had deferred tax assets of $7.9 million and $7.2 million as of December 31, 2019 and 2018, respectively, related to non-Canadian foreign net operating loss carryforwards. These net operating loss carryforwards expire beginning in 2020 through 2029, while some may be carried forward indefinitely. As of December 31, 2019 and 2018, WESCO had deferred tax assets of $2.6 million and $3.2 million, respectively, related to state net operating loss carryforwards. These carryforwards expire beginning in 2022 through 2037. The Company has determined, based upon an evaluation of all available evidence, that certain non-Canadian foreign net operating loss carryforwards will not be realized before they expire. Accordingly, the Company recorded a full valuation allowance against deferred tax assets related to certain non-Canadian foreign net operating loss carryforwards of $4.6 million and $4.1 million at December 31, 2019 and 2018, respectively.

As of December 31, 2019, WESCO had a deferred tax asset of $1.2 million related to foreign tax credit carryforwards. The foreign tax credit carryforwards expire beginning in 2028. The Company determined, based upon an evaluation of all available evidence, that the foreign tax credit carryforwards will not be realized before they expire. Accordingly, the Company recorded a full valuation allowance against the deferred tax asset related to foreign tax credit carryforwards of $1.2 million at December 31, 2019.

The Company is under examination by tax authorities in the U.S. and Canada and remains subject to examination until the applicable statutes of limitation expire. The statutes of limitation for the material jurisdictions in which the Company files income tax returns remain open as follows:



United States — Federal		2015 and forward
United States — Material States		2015 and forward
Canada		2008 and forward

The following table sets forth the reconciliation of gross unrecognized tax benefits:



	As of December 31,
	2019			2018			2017
	(In thousands)
Beginning balance January 1	$	1,293		$	4,348		$	6,181
Reductions for tax positions of prior years	—			—			(155		)
Settlements	(1,290		)	(2,646		)	(1,025		)
Lapse in statute of limitations	—			(287		)	(755		)
Foreign currency exchange rate changes	51			(122		)	102
Ending balance December 31	$	54		$	1,293		$	4,348

The total amount of unrecognized tax benefits were $0.1 million, $1.3 million, and $4.3 million as of December 31, 2019, 2018 and 2017, respectively. The amount of unrecognized tax benefits that would affect the effective tax rate if recognized in the consolidated financial statements was $0.1 million, $1.3 million, and $1.7 million, respectively. It is not expected that the amount of unrecognized tax benefits will change within the next twelve months.

The Company classifies interest related to unrecognized tax benefits as a component of net interest and other in the Consolidated Statement of Income and Comprehensive Income. The Company recognized interest income on unrecognized tax benefits of $0.8 million in 2019. In 2018 and 2017, interest expense on unrecognized tax benefits was $0.2 million and $0.1 million, respectively. As of December 31, 2019 and 2018, WESCO had a liability of $0.1 million and $0.8 million, respectively, for interest expense related to unrecognized tax benefits. The Company classifies penalties related to unrecognized tax benefits as part of income tax expense. Penalties recorded in income tax expense were immaterial in 2019, 2018, and 2017.

EARNINGS PER SHARE EARNINGS PER SHARE

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

EARNINGS PER SHARE

13. EARNINGS PER SHARE

Basic earnings per share is computed by dividing net income attributable to WESCO International by the weighted-average number of common shares outstanding during the periods. Diluted earnings per share is computed by dividing net income attributable to WESCO International by the weighted-average common shares and common share equivalents outstanding during the periods. The dilutive effect of common share equivalents is considered in the diluted earnings per share computation using the treasury stock method, which includes consideration of equity awards.

The following table sets forth the details of basic and diluted earnings per share:



	Year Ended December 31,
	2019		2018		2017
(In thousands, except per share data)
Net income attributable to WESCO International	$	223,426	$	227,343	$	163,460
Weighted-average common shares outstanding used in computing basic earnings per share	43,104		46,722		47,849
Common shares issuable upon exercise of dilutive equity awards	383		477		512
Weighted-average common shares outstanding and common share equivalents used in computing diluted earnings per share	43,487		47,199		48,361
Earnings per share attributable to WESCO International
Basic	$	5.18	$	4.87	$	3.42
Diluted	$	5.14	$	4.82	$	3.38

The computation of diluted earnings per share attributable to WESCO International excluded equity awards of approximately 1.7 million, 1.6 million and 1.3 million for the years ended December 31, 2019, 2018 and 2017, respectively. These shares were excluded because their effect would have been antidilutive.

In December 2014, the Company's Board of Directors (the "Board") authorized the repurchase of up to $300 million of the Company's common stock through December 31, 2017 (the "2014 Repurchase Authorization"). During the year ended December 31, 2017, the Company repurchased 1,778,537 shares for $100.0 million.

In December 2017, the Board authorized the repurchase of up to $300 million of the Company's common stock through December 31, 2020 (the "2017 Repurchase Authorization"). In October 2018, the Board approved an increase to the 2017 Repurchase Authorization from $300 million to $400 million. During the year ended December 31, 2018, the Company entered into accelerated stock repurchase agreements with a financial institution to repurchase shares of its common stock pursuant to its 2017 Repurchase Authorization. In exchange for up-front cash payments totaling $125.0 million, the Company received 2,368,738 shares, of which 365,272 shares were settled in 2019.

On May 7, 2019, the Company entered into an accelerated stock repurchase agreement with a financial institution to repurchase additional shares of its common stock pursuant to the 2017 Repurchase Authorization. In exchange for an up-front cash payment of $150.0 million, the Company received a total of 3,090,312 shares. As of December 31, 2019, WESCO had repurchased 5,459,030 shares of common stock for $275.0 million under the 2017 Repurchase Authorization.

The total number of shares ultimately delivered under the accelerated stock repurchase transactions described above were determined by the average of the volume-weighted-average price of the Company's common stock for each exchange business day during the respective settlement valuation periods. WESCO funded the repurchases with available cash, and borrowings under its accounts receivable securitization and revolving credit facilities. For purposes of computing earnings per share, share repurchases have been reflected as a reduction to common shares outstanding on the respective delivery dates.

STOCK-BASED COMPENSATION STOCK-BASED COMPENSATION

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

STOCK-BASED COMPENSATION

15. STOCK-BASED COMPENSATION

WESCO sponsors a stock-based compensation plan. The 1999 Long-Term Incentive Plan, as amended and restated (the “LTIP”) was designed to be the successor plan to all prior plans. Any shares remaining reserved for future issuance under the prior plans are available for issuance under the LTIP. The LTIP is administered by the Compensation Committee of the Board.

On May 31, 2017, the Company renewed and restated the LTIP, increasing the maximum number of shares of common stock that may be issued under the plan by 1.7 million shares to 3.4 million. Under the LTIP, the total number of shares of common stock authorized to be issued will be reduced by 1 share of common stock for every 1 share that is subject to a stock appreciation right granted, and 1.83 shares of common stock for every 1 share that is subject to an award other than a stock appreciation right granted on or after May 31, 2017. As of December 31, 2019, 2.6 million shares of common stock were reserved under the LTIP for future equity award grants.

WESCO’s stock-based employee compensation plans are comprised of stock-settled stock appreciation rights, restricted stock units and performance-based awards. Compensation cost for all stock-based awards is measured at fair value on the date of grant and compensation cost is recognized, net of estimated forfeitures, over the service period for awards expected to vest. The fair value of stock-settled stock appreciation rights and performance-based awards with market conditions is determined using the Black-Scholes and Monte Carlo simulation models, respectively. The fair value of restricted stock units and performance-based awards with performance conditions is determined by the grant-date closing price of WESCO’s common stock. The forfeiture assumption is based on WESCO’s historical employee behavior that is reviewed on an annual basis. No dividends are assumed. For stock-settled stock appreciation rights that are exercised and for restricted stock units and performance-based awards that vest, shares are issued out of WESCO's outstanding common stock.

Stock-settled stock appreciation rights vest ratably over a three-year period and terminate on the tenth anniversary of the grant date unless terminated sooner under certain conditions. Vesting of restricted stock units is based on a minimum time period of three years. Vesting of performance-based awards is based on a three-year performance period, and the number of shares earned, if any, depends on the attainment of certain performance levels. Outstanding awards would vest upon the consummation of a change in control transaction and performance-based awards would vest at the target level.

Performance-based awards granted in 2019 were based on two equally-weighted performance measures: the three-year average growth rate of WESCO's net income and the three-year cumulative return on net assets. Performance-based awards granted in 2018 were based on two equally-weighted performance measures: the three-year average growth rate of the Company’s fully diluted earnings per share and the three-year cumulative return on net assets. From 2015 to 2017, the two equally-weighted performance-based award metrics were the three-year average growth rate of WESCO's net income and WESCO's total stockholder return in relation to the total stockholder return of a select group of peer companies over a three-year period.

WESCO recognized $19.1 million, $16.4 million and $14.8 million of non-cash stock-based compensation expense, which is included in selling, general and administrative expenses, for the years ended December 31, 2019, 2018 and 2017, respectively. As of December 31, 2019, there was $20.7 million of total unrecognized compensation expense related to non-vested stock-based compensation arrangements for all awards previously made of which approximately $13.0 million is expected to be recognized in 2020, $6.9 million in 2021 and $0.8 million in 2022.

The total intrinsic value of awards exercised during the years ended December 31, 2019, 2018, and 2017 was $10.7 million, $8.2 million, and $17.2 million, respectively. The gross deferred tax benefit associated with the exercise of stock-based awards totaled $2.5 million, $2.0 million, and $6.4 million in 2019, 2018, and 2017, respectively.

The following table sets forth a summary of stock-settled stock appreciation rights and related information for the periods presented:



	Year Ended December 31,
	2019							2018				2017
	Awards		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life	Aggregate Intrinsic Value (In thousands)		Awards		Weighted-Average Exercise Price		Awards		Weighted-Average Exercise Price
Beginning of year	2,351,633		$	59.26				2,238,607		$	57.75	2,439,487		$	52.62
Granted	213,618		54.63					509,046		62.68		455,807		71.21
Exercised	(113,099	)	35.01					(192,700	)	40.74		(495,181	)	42.19
Canceled	(115,103	)	65.27					(203,320	)	68.69		(161,506	)	66.06
End of year	2,337,049		59.72		5.6	$	13,039	2,351,633		59.26		2,238,607		57.75
Exercisable at end of year	1,723,370		$	59.00	4.7	$	12,053	1,453,932		$	57.93	1,331,580		$	56.96

The following table sets forth the weighted-average assumptions used to estimate the fair value of stock-settled stock appreciation rights granted during the periods presented:



	Year Ended December 31,
	2019	2018	2017
Stock-settled stock appreciation rights granted	213,618	509,046	455,807
Risk free interest rate	2.5%	2.5%	1.9%
Expected life (in years)	5	5	5
Expected volatility	29%	28%	29%

The risk-free interest rate is based on the U.S. Treasury Daily Yield Curve rate as of the grant date. The expected life is based on historical exercise experience and the expected volatility is based on the volatility of the Company's daily stock prices over a five-year period preceding the grant date.

The weighted-average fair value per stock-settled stock appreciation right granted was $16.36, $18.38 and $20.52 for the years ended December 31, 2019, 2018 and 2017, respectively.

The following table sets forth a summary of time-based restricted stock units and related information for the periods presented:



	Year Ended December 31,
	2019				2018				2017
	Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value
Unvested at beginning of year	327,798		$	57.87	290,054		$	58.11	257,096		$	57.47
Granted	192,106		54.13		122,062		62.40		100,993		71.33
Vested	(136,777	)	46.52		(64,166	)	67.91		(44,720	)	84.57
Forfeited	(19,398	)	59.62		(20,152	)	58.15		(23,315	)	57.52
Unvested at end of year	363,729		$	60.00	327,798		$	57.87	290,054		$	58.11

The following table sets forth a summary of performance-based awards and related information for the periods presented:



	Year Ended December 31,
	2019				2018				2017
	Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value
Unvested at beginning of year	138,896		$	59.33	148,508		$	60.23	149,320		$	60.36
Granted	126,874		54.64		44,144		62.80		39,978		76.63
Vested	(25,696	)	42.44		—		—		—		—
Forfeited	(44,769	)	52.11		(53,756	)	64.67		(40,790	)	76.77
Unvested at end of year	195,305		$	60.24	138,896		$	59.33	148,508		$	60.23

The following table sets forth the assumptions used to estimate the fair value of performance shares granted during the periods presented:



	Year ended December 31,
	2019		2018		2017
Grant date share price	$	54.64	$	62.80	$	71.67
WESCO expected volatility	n/a		n/a		29		%
Peer group median volatility	n/a		n/a		24		%
Risk-free interest rate	n/a		n/a		1.5		%
Correlation of peer company returns	n/a		n/a		114		%

The unvested performance-based awards in the table above include 17,507 shares in which vesting of the ultimate number of shares is dependent upon WESCO's total stockholder return in relation to the total stockholder return of a select group of peer companies over a three-year period. These awards are accounted for as awards with market conditions; compensation cost is recognized over the service period, regardless of whether the market conditions are achieved and the awards ultimately vest.

Vesting of the remaining 177,798 shares of performance-based awards in the table above is dependent upon the achievement of certain performance targets, including 77,856 that are dependent upon the three-year average growth rate of WESCO's net income, 19,797 that are dependent upon the three-year average growth rate of the Company's fully diluted earnings per share, and 80,145 that are based upon the three-year cumulative return on net assets. These awards are accounted for as awards with performance conditions; compensation cost is recognized over the performance period based upon WESCO's determination of whether it is probable that the performance targets will be achieved.

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	16. COMMITMENTS AND CONTINGENCIES From time to time, a number of lawsuits and claims have been or may be asserted against the Company relating to the conduct of its business, including litigation relating to commercial, product and employment matters. The outcome of any litigation cannot be predicted with certainty, and some lawsuits may be determined adversely to WESCO. However, management does not believe that the ultimate outcome of any such pending matters is likely to have a material adverse effect on WESCO's financial condition or liquidity, although the resolution in any fiscal period of one or more of these matters may have a material adverse effect on WESCO's results of operations for that period. In an effort to expand the Company's footprint in the Middle East, WESCO has been doing business since 2009 with WESTEC Supplies General Trading (“WESTEC”), an industrial equipment supplier headquartered in the United Arab Emirates. WESTEC has debt facilities comprised of a $5.8 million term loan and a $1.1 million line of credit to support its working capital requirements and joint sales efforts with WESCO. Due to the nature of WESCO’s arrangement with WESTEC, WESCO has provided a standby letter of credit under its revolving credit facility of up to $7.3 million as security for WESTEC’s debt facilities. As of December 31, 2019, WESTEC had outstanding indebtedness totaling $6.3 million. Management currently believes the estimated fair value of the noncontingent guarantee on the outstanding indebtedness is nominal and therefore a liability has not been recorded as of December 31, 2019.

SEGMENTS AND RELATED INFORMATION

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

SEGMENTS AND RELATED INFORMATION

17. SEGMENTS AND RELATED INFORMATION

WESCO distributes products and provides services through its four operating segments, which have been aggregated as one reportable segment. WESCO has approximately 200,000 unique product stock keeping units and markets more than 1,000,000 products for customers. There were no material amounts of sales or transfers among geographic areas and no material amounts of export sales.

WESCO attributes revenues from external customers to individual countries on the basis of the point of sale. The following table sets forth information about WESCO by geographic area:



	Net Sales Year Ended December 31,												Long-Lived Assets⁽¹⁾ December 31,
	2019				2018				2017				2019		2018		2017
(In thousands)	(In thousands)												(In thousands)
United States	$	6,234,119	75	%	$	6,089,130	75	%	$	5,775,988	75	%	$	315,288	$	106,078	$	95,851
Canada⁽²⁾	1,647,066		20	%	1,647,933		20	%	1,521,378		20	%	95,642		50,877		56,591
Other International⁽²⁾	477,732		5	%	439,538		5	%	381,655		5	%	6,352		3,923		4,003
Total	$	8,358,917			$	8,176,601			$	7,679,021			$	417,282	$	160,878	$	156,445


⁽¹⁾	As described in Note 2, effective January 1, 2019, the Company adopted Topic 842 using the effective date method. The adoption of Topic 842 resulted in the recognition of right-of-use assets in the balance sheet. As of December 31, 2019, long-lived assets include $235.8 million of operating lease assets.


⁽²⁾	The prior period has been reclassified to confirm to the current period presentation.

The following table sets forth information about WESCO’s sales by product category:



	Year Ended December 31,
	2019	2018	2017
(percentages based on total sales)
General Supplies	41%	40%	40%
Wire, Cable and Conduit	14%	14%	15%
Communications and Security	16%	16%	15%
Electrical Distribution and Controls	10%	11%	10%
Lighting and Sustainability	11%	11%	12%
Automation, Controls and Motors	8%	8%	8%

OTHER FINANCIAL INFORMATION

12 Months Ended

Dec. 31, 2019

Condensed Financial Information [Abstract]

OTHER FINANCIAL INFORMATION

18. CONDENSED CONSOLIDATING FINANCIAL INFORMATION

WESCO Distribution has outstanding $500 million in aggregate principal amount of 2021 Notes and $350 million in aggregate principal amount of 2024 Notes. The 2021 Notes and 2024 Notes are unsecured senior obligations of WESCO Distribution and are fully and unconditionally guaranteed on a senior unsecured basis by WESCO International.

Condensed consolidating financial information for WESCO International, WESCO Distribution and the non-guarantor subsidiaries is presented in the following tables.



	Condensed Consolidating Balance Sheet
	December 31, 2019
	(In thousands)
	WESCO International, Inc.		WESCO Distribution, Inc.		Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Cash and cash equivalents	$	—	$	46,499	$	104,403		$	—		$	150,902
Trade accounts receivable, net	—		—		1,187,359			—			1,187,359
Inventories	—		490,071		521,603			—			1,011,674
Prepaid expenses and other current assets	1,124		44,382		144,084			886			190,476
Total current assets	1,124		580,952		1,957,449			886			2,540,411
Intercompany receivables, net	—		—		2,668,314			(2,668,314		)	—
Property, buildings and equipment, net	—		82,753		98,695			—			181,448
Operating lease assets	—		141,824		94,010			—			235,834
Intangible assets, net	—		1,500		285,775			—			287,275
Goodwill	—		257,623		1,501,417			—			1,759,040
Investments in affiliates	3,451,020		5,379,728		—			(8,830,748		)	—
Other assets	—		854		12,773			—			13,627
Total assets	$	3,452,144	$	6,445,234	$	6,618,433		$	(11,498,176	)	$	5,017,635

Accounts payable	$	—	$	402,174	$	428,304		$	—		$	830,478
Short-term debt	—		—		26,255			—			26,255
Other current liabilities	—		42,901		183,539			886			227,326
Total current liabilities	—		445,075		638,098			886			1,084,059
Intercompany payables, net	1,186,661		1,481,653		—			(2,668,314		)	—
Long-term debt	—		842,708		414,359			—			1,257,067
Operating lease liabilities	—		111,291		68,539			—			179,830
Other noncurrent liabilities	—		113,487		124,521			—			238,008
Total WESCO International stockholders’ equity	2,265,483		3,451,020		5,379,728			(8,830,748		)	2,265,483
Noncontrolling interests	—		—		(6,812		)	—			(6,812		)
Total liabilities and stockholders’ equity	$	3,452,144	$	6,445,234	$	6,618,433		$	(11,498,176	)	$	5,017,635



	Condensed Consolidating Balance Sheet
	December 31, 2018
	(In thousands)
	WESCO International, Inc.		WESCO Distribution, Inc.		Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Cash and cash equivalents	$	—	$	35,931	$	60,412		$	—		$	96,343
Trade accounts receivable, net	—		—		1,166,607			—			1,166,607
Inventories	—		440,422		508,304			—			948,726
Prepaid expenses and other current assets	1,123		57,586		124,523			(9,268		)	173,964
Total current assets	1,123		533,939		1,859,846			(9,268		)	2,385,640
Intercompany receivables, net	—		—		2,403,704			(2,403,704		)	—
Property, buildings and equipment, net	—		63,506		97,372			—			160,878
Intangible assets, net	—		2,131		313,885			—			316,016
Goodwill	—		257,623		1,464,980			—			1,722,603
Investments in affiliates	3,188,124		5,137,783		—			(8,325,907		)	—
Other assets	—		2,905		16,994			—			19,899
Total assets	$	3,189,247	$	5,997,887	$	6,156,781		$	(10,738,879	)	$	4,605,036

Accounts payable	$	—	$	404,373	$	389,975		$	—		$	794,348
Short-term debt	—		—		30,785			—			30,785
Other current liabilities	—		86,600		159,481			(9,268		)	236,813
Total current liabilities	—		490,973		580,241			(9,268		)	1,061,946
Intercompany payables, net	1,053,937		1,349,767		—			(2,403,704		)	—
Long-term debt	—		842,093		325,218			—			1,167,311
Other noncurrent liabilities	—		126,930		119,123			—			246,053
Total WESCO International stockholders’ equity	2,135,310		3,188,124		5,137,783			(8,325,907		)	2,135,310
Noncontrolling interests	—		—		(5,584		)	—			(5,584		)
Total liabilities and stockholders’ equity	$	3,189,247	$	5,997,887	$	6,156,781		$	(10,738,879	)	$	4,605,036

Reclassification

Certain reclassifications have been made to conform the presentation of previously reported amounts to that of the current period.



	Condensed Consolidating Statement of Income and Comprehensive Income
	Year ended December 31, 2019
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net sales	$	—		$	3,642,413		$	4,899,987		$	(183,483	)	$	8,358,917
Cost of goods sold (excluding depreciation and	—			2,954,246			4,006,693			(183,483		)	6,777,456
amortization)
Selling, general and administrative expenses	—			593,025			580,112			—			1,173,137
Depreciation and amortization	—			19,155			42,952			—			62,107
Results of affiliates’ operations	222,198			201,247			—			(423,445		)	—
Net interest and other	—			49,392			14,764			—			64,156
Provision for income taxes	—			5,644			54,219			—			59,863
Net income	222,198			222,198			201,247			(423,445		)	222,198
Less: Net loss attributable to noncontrolling interests	—			—			(1,228		)	—			(1,228		)
Net income attributable to WESCO International	$	222,198		$	222,198		$	202,475		$	(423,445	)	$	223,426
Other comprehensive income (loss):
Foreign currency translation adjustments	49,306			49,306			49,306			(98,612		)	49,306
Post retirement benefit plan adjustments, net of tax	(8,643		)	(8,643		)	(8,643		)	17,286			(8,643		)
Comprehensive income attributable to WESCO International	$	262,861		$	262,861		$	243,138		$	(504,771	)	$	264,089



	Condensed Consolidating Statement of Income and Comprehensive Income
	Year ended December 31, 2018
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net sales	$	—		$	3,572,406		$	4,757,321		$	(153,126	)	$	8,176,601
Cost of goods sold (excluding depreciation and	—			2,890,490			3,871,856			(153,126		)	6,609,220
amortization)
Selling, general and administrative expenses	—			590,009			561,935			—			1,151,944
Depreciation and amortization	—			18,334			44,663			—			62,997
Results of affiliates’ operations	225,355			209,802			—			(435,157		)	—
Net interest and other	—			54,178			17,237			—			71,415
Provision for income taxes	—			3,842			51,828			—			55,670
Net income	225,355			225,355			209,802			(435,157		)	225,355
Less: Net loss attributable to noncontrolling interests	—			—			(1,988		)	—			(1,988		)
Net income attributable to WESCO International	$	225,355		$	225,355		$	211,790		$	(435,157	)	$	227,343
Other comprehensive income (loss):
Foreign currency translation adjustments	(99,643		)	(99,643		)	(99,643		)	199,286			(99,643		)
Post retirement benefit plan adjustments, net of tax	3,798			3,798			3,798			(7,596		)	3,798
Comprehensive income attributable to WESCO International	$	129,510		$	129,510		$	115,945		$	(243,467	)	$	131,498



	Condensed Consolidating Statement of Income and Comprehensive Income
	Year ended December 31, 2017
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net sales	$	—		$	3,370,088		$	4,441,655		$	(132,722	)	$	7,679,021
Cost of goods sold (excluding depreciation and	—			2,714,511			3,612,577			(132,722		)	6,194,366
amortization)
Selling, general and administrative expenses	—			555,503			546,095			—			1,101,598
Depreciation and amortization	—			18,442			45,575			—			64,017
Results of affiliates’ operations	160,587			168,782			—			(329,369		)	—
Net interest and other	—			94,313			(27,713		)	—			66,600
Provision for income taxes	(2,546		)	(4,486		)	96,339			—			89,307
Net income	$	163,133		$	160,587		$	168,782		$	(329,369	)	$	163,133
Less: Net loss attributable to noncontrolling interests	—			—			(327		)	—			(327		)
Net income attributable to WESCO International	$	163,133		$	160,587		$	169,109		$	(329,369	)	$	163,460
Other comprehensive income (loss):
Foreign currency translation adjustments	85,762			85,762			85,762			(171,524		)	85,762
Post retirement benefit plan adjustments, net of tax	(6,381		)	(6,381		)	(6,381		)	12,762			(6,381		)
Comprehensive income attributable to WESCO International	$	242,514		$	239,968		$	248,490		$	(488,131	)	$	242,841



	Condensed Consolidating Statement of Cash Flows
	Year ended December 31, 2019
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net cash provided by operating activities	$	20,328		$	188,797		$	15,242		$	—		$	224,367
Investing activities:
Capital expenditures	—			(22,330		)	(21,737		)	—			(44,067		)
Acquisition payments	—			(27,597		)	—			—			(27,597		)
Proceeds from sale of assets	—			—			16,795			—			16,795
Dividends received from subsidiaries	—			134,853			—			(134,853		)	—
Advances to subsidiaries and other	—			(222,482		)	(5,931		)	222,482			(5,931		)
Net cash used in investing activities	—			(137,556		)	(10,873		)	87,629			(60,800		)
Financing activities:
Proceeds from issuance of debt	132,721			423,441			998,019			(222,482		)	1,331,699
Repayments of debt	—			(449,190		)	(824,302		)	—			(1,273,492		)
Equity activities	(153,049		)	—			—			—			(153,049		)
Dividends paid by subsidiaries	—			—			(134,853		)	134,853			—
Other	—			(14,924		)	—			—			(14,924		)
Net cash (used in) provided by financing activities	(20,328		)	(40,673		)	38,864			(87,629		)	(109,766		)
Effect of exchange rate changes on cash and cash equivalents	—			—			758			—			758
Net change in cash and cash equivalents	—			10,568			43,991			—			54,559
Cash and cash equivalents at the beginning of period	—			35,931			60,412			—			96,343
Cash and cash equivalents at the end of period	$	—		$	46,499		$	104,403		$	—		$	150,902



	Condensed Consolidating Statement of Cash Flows
	Year ended December 31, 2018
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net cash provided by operating activities	$	18,672		$	153,467		$	124,582		$	—		$	296,721
Investing activities:
Capital expenditures	—			(17,573		)	(18,637		)	—			(36,210		)
Proceeds from sale of assets	—			—			12,461			—			12,461
Dividends received from subsidiaries	—			347,531			—			(347,531		)	—
Advances to subsidiaries and other	—			(406,028		)	196,219			199,416			(10,393		)
Net cash (used in) provided by investing activities	—			(76,070		)	190,043			(148,115		)	(34,142		)
Financing activities:
Proceeds from issuance of debt	108,497			339,606			1,086,673			(199,416		)	1,335,360
Repayments of debt	—			(410,606		)	(1,051,611		)	—			(1,462,217		)
Equity activities	(127,169		)	—			—			—			(127,169		)
Dividends paid by subsidiaries	—			—			(347,531		)	347,531			—
Other	—			(21,068		)	—			—			(21,068		)
Net cash used in financing activities	(18,672		)	(92,068		)	(312,469		)	148,115			(275,094		)
Effect of exchange rate changes on cash and cash equivalents	—			—			(9,095		)	—			(9,095		)
Net change in cash and cash equivalents	—			(14,671		)	(6,939		)	—			(21,610		)
Cash and cash equivalents at the beginning of period	—			50,602			67,351			—			117,953
Cash and cash equivalents at the end of period	$	—		$	35,931		$	60,412		$	—		$	96,343



	Condensed Consolidating Statement of Cash Flows
	Year ended December 31, 2017
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net cash (used in) provided by operating activities	$	(36,575	)	$	101,826		$	83,871		$	—		$	149,122
Investing activities:
Capital expenditures	—			(13,215		)	(8,292		)	—			(21,507		)
Proceeds from sale of assets	—			—			6,766			—			6,766
Dividends received from subsidiaries	—			307,784			—			(307,784		)	—
Advances to subsidiaries and other	—			(383,686		)	26,912			366,220			9,446
Net cash (used in) provided by investing activities	—			(89,117		)	25,386			58,436			(5,295		)
Financing activities:
Proceeds from issuance of debt	143,367			775,926			1,144,848			(383,686		)	1,680,455
Repayments of debt	—			(785,392		)	(952,740		)	17,466			(1,720,666		)
Equity activities	(106,792		)	—			—			—			(106,792		)
Dividends paid by subsidiaries	—			—			(307,784		)	307,784			—
Other	—			5,807			—			—			5,807
Net cash provided by (used in) financing activities	36,575			(3,659		)	(115,676		)	(58,436		)	(141,196		)
Effect of exchange rate changes on cash and cash equivalents	—			—			5,191			—			5,191
Net change in cash and cash equivalents	—			9,050			(1,228		)	—			7,822
Cash and cash equivalents at the beginning of period	—			41,552			68,579			—			110,131
Cash and cash equivalents at the end of period	$	—		$	50,602		$	67,351		$	—		$	117,953

SELECTED QUARTERLY FINANCIAL DATA

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

SELECTED QUARTERLY FINANCIAL DATA

. SELECTED QUARTERLY FINANCIAL DATA (unaudited)

The following table sets forth selected quarterly financial data for the years ended December 31, 2019 and 2018:



	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
2019
Net Sales	$	1,961,267	$	2,150,088	$	2,148,110	$	2,099,452
Cost of goods sold (excluding depreciation and amortization)	1,578,771		1,741,114		1,747,913		1,709,658
Income from operations	70,726		97,950		93,733		83,808
Income before income taxes	53,606		80,643		80,225		67,587
Net income	41,950		63,215		64,339		52,694
Net income attributable to WESCO International	42,369		63,464		64,495		53,098
Basic earnings per share attributable to WESCO International⁽¹⁾	0.94		1.46		1.53		1.27
Diluted earnings per share attributable to WESCO International⁽²⁾	0.93		1.45		1.52		1.26

2018
Net Sales	$	1,993,915	$	2,103,994	$	2,067,245	$	2,011,447
Cost of goods sold (excluding depreciation and amortization)	1,613,966		1,704,100		1,670,037		1,621,117
Income from operations	73,241		91,183		97,517		90,499
Income before income taxes	53,458		73,442		80,467		73,658
Net income	42,971		57,673		66,645		58,066
Net income attributable to WESCO International	44,421		57,940		66,849		58,133
Basic earnings per share attributable to WESCO International⁽¹⁾	0.94		1.23		1.42		1.27
Diluted earnings per share attributable to WESCO International⁽²⁾	0.93		1.22		1.41		1.26


⁽¹⁾	Earnings per share (EPS) in each quarter is computed using the weighted-average number of shares outstanding during that quarter while EPS for the full year is computed by using the weighted-average number of shares outstanding during the year. Thus, the sum of the four quarters’ EPS may not equal the full-year EPS.

⁽²⁾

Diluted EPS in each quarter is computed using the weighted-average number of shares outstanding and common share equivalents during that quarter while diluted EPS for the full year is computed by using the weighted-average number of shares outstanding and common share equivalents during the year. Thus, the sum of the four quarters’ diluted EPS may not equal the full-year diluted EPS.

SUBSEQUENT EVENT	12 Months Ended
SUBSEQUENT EVENT	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events [Text Block]	20. SUBSEQUENT EVENTS On January 10, 2020, WESCO International entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Anixter International Inc. (“Anixter”) and Warrior Merger Sub, Inc., a wholly owned subsidiary of WESCO International (“Merger Sub”). The Merger Agreement provides that, among other things and subject to the terms and conditions of the Merger Agreement, Merger Sub will be merged with and into Anixter (the “Merger”), with Anixter surviving the Merger and continuing as a wholly owned subsidiary of WESCO International. At the effective time of the Merger, each outstanding share of Anixter common stock will be converted into the right to receive $70.00 in cash, 0.2397 shares of WESCO International common stock, and 0.6356 depositary shares of preferred stock, each share representing a 1/1,000th interest in a share of newly issued WESCO Series A fixed-rate reset cumulative perpetual preferred stock, $25,000 stated amount per whole preferred share (subject to adjustment as set forth in the merger agreement). Based on the closing price of WESCO common stock on January 10, 2020, the last full trading day before the public announcement of the merger, and the liquidation preference of the WESCO Series A preferred stock underlying the preferred stock consideration, and giving effect to the downside protection described in the merger agreement, the implied value of the merger consideration is $100.00 per Anixter share.

Schedule II - Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2018

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

Schedule II - Valuation and Qualifying Accounts

Schedule II—Valuation and Qualifying Accounts



	Balance at Beginning		Charged to	Charged to Other			Balance at
	of Period		Expense	Accounts⁽¹⁾	Deductions⁽²⁾		End of Period
Allowance for doubtful accounts	(In thousands)
Year ended December 31, 2019	$	24,468	7,006	52	(6,083	)	$	25,443
Year ended December 31, 2018	21,313		10,854	—	(7,699	)	24,468
Year ended December 31, 2017	22,007		8,466	—	(9,160	)	21,313

_________________________


⁽¹⁾	Represents allowance for doubtful accounts in connection with certain acquisitions and divestitures.

⁽²⁾

Includes a reduction in the allowance for doubtful accounts due to write-off of accounts receivable.

ACCOUNTING POLICIES (Policies)	12 Months Ended
ACCOUNTING POLICIES (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Consolidation	Basis of Consolidation The consolidated financial statements include the accounts of WESCO International and all of its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates are based on management’s best knowledge of current events and actions WESCO may undertake in the future, actual results may ultimately differ from the estimates.
Revenue Recognition	Revenue Recognition WESCO’s revenue arrangements generally consist of single performance obligations to transfer a promised good or service, or a combination of goods and services. Revenue is recognized when control has transferred to the customer, which is generally when the product has shipped from a WESCO facility or directly from a supplier. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. Revenue for integrated supply services is recognized over time based on hours incurred as the transfer of control occurs as the services are being performed. WESCO generally satisfies its performance obligations within a year or less. WESCO generally does not have significant financing terms associated with its contracts; payments are normally received within 60 days. There are generally no significant costs associated with obtaining customer contracts. WESCO generally passes through warranties offered by manufacturers or suppliers to its customers. Sales taxes (and value added taxes in foreign jurisdictions) collected from customers and remitted to governmental authorities are excluded from net sales.
Supplier Volume Rebates	Supplier Volume Rebates WESCO receives volume rebates from certain suppliers based on contractual arrangements with such suppliers. Volume rebates are included within other accounts receivable in the Consolidated Balance Sheets, and represent the estimated amounts due to WESCO based on forecasted purchases and the rebate provisions of the various supplier contracts. The corresponding rebate income is recorded as a reduction to cost of goods sold. Receivables under the supplier rebate program were $81.6 million at December 31, 2019 and $73.5 million at December 31, 2018. The supplier volume rebate as a percentage of net sales was 1.2% in 2019, and 1.3% in 2018 and 2017.
Shipping and Handling Costs and Fees	Shipping and handling costs are recognized in net sales when they are billed to the customer. These costs are recognized as a component of selling, general and administrative expenses when WESCO does not bill the customer. WESCO has elected to recognize shipping and handling costs as a fulfillment cost. Shipping and handling costs recorded as a component of selling, general and administrative expenses totaled $71.7 million, $74.1 million and $61.8 million for the years ended December 31, 2019, 2018 and 2017, respectively.
Cash Equivalents	Cash Equivalents Cash equivalents are defined as highly liquid investments with original maturities of 90 days or less when purchased.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts WESCO maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. WESCO has a systematic procedure using historical data and reasonable assumptions of collectability made at the local branch level and on a consolidated corporate basis to estimate allowances for doubtful accounts. If the financial condition of WESCO’s customers were to deteriorate, resulting in an impairment of their ability to make payments, additional allowances may be required. The allowance for doubtful accounts was $25.4 million at December 31, 2019 and $24.5 million at December 31, 2018. The total amount recorded as selling, general and administrative expense related to bad debts was $7.0 million, $10.9 million and $8.5 million for 2019, 2018 and 2017, respectively.
Inventories	Inventories Inventories primarily consist of merchandise purchased for resale and are stated at the lower of cost and net realizable value. Cost is determined principally under the average cost method. WESCO makes provisions for obsolete or slow-moving inventories as necessary to reflect reductions in value. WESCO writes down its inventories to net realizable value based on internal factors derived from historical analysis of actual losses. WESCO uses past data to identify items in excess of 36 months supply relative to demand or movement. WESCO then analyzes the ultimate disposition of identified excess inventories as they are sold, returned to supplier, or scrapped. This historical item-by-item analysis allows WESCO to develop an estimate of the likelihood that an item identified as being in excess supply ultimately becomes obsolete. WESCO applies the estimate to inventories currently in excess of 36 months supply, and reduces the carrying value of its inventories by the derived amount. Reserves for excess and obsolete inventories were $30.7 million and $27.6 million at December 31, 2019 and 2018, respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $10.0 million, $9.7 million and $8.8 million for 2019, 2018 and 2017, respectively. WESCO absorbs into the cost of inventories certain overhead expenses such as purchasing, receiving and storage and at December 31, 2019 and 2018, $71.2 million and $69.2 million, respectively, of these costs were included in ending inventories.
Property, Buildings and Equipment	Property, Buildings and Equipment Property, buildings and equipment are recorded at cost. Depreciation expense is determined using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over either their respective lease terms or their estimated lives, whichever is shorter. Estimated useful lives range from five to forty years for buildings and leasehold improvements and three to ten years for furniture, fixtures and equipment. Capitalized computer software costs are amortized using the straight-line method over the estimated useful life, typically three to five years, and are reported at the lower of unamortized cost or net realizable value. Expenditures for new facilities and improvements that extend the useful life of an asset are capitalized. Ordinary repairs and maintenance are expensed as incurred. When property is retired or otherwise disposed of, the cost and the related accumulated depreciation are removed from the accounts and any resulting gains or losses are recorded and reported as selling, general and administrative expenses. Of WESCO’s $181.4 million net book value of property, buildings and equipment as of December 31, 2019, $88.1 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 500 branches and 11 distribution centers, mitigating the risk of impairment. WESCO assesses its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of any such assets may not be fully recoverable. Changes in circumstances include technological advances, changes in the business model, capital structure, economic conditions or operating performance. The evaluation is based upon, among other things, utilization, serviceability and assumptions about the estimated future undiscounted cash flows that these assets are expected to generate. When the sum of the undiscounted cash flows is less than the carrying value of the asset or asset group, an impairment loss is recognized to the extent that carrying value exceeds fair value. Management applies its best judgment when performing these evaluations.
Goodwill and Intangible Assets	Goodwill and Indefinite-Lived Intangible Assets Goodwill and indefinite-lived intangible assets are tested for impairment annually during the fourth quarter using information available at the end of September, or more frequently if triggering events occur, indicating that their carrying value may not be recoverable. WESCO tests for goodwill impairment on a reporting unit level and the evaluation involves comparing the fair value of each reporting unit to its carrying value. The fair values of the reporting units are determined using a combination of a discounted cash flow analysis and market multiples. Assumptions used for these fair value techniques, including expected operating margin and discount rate, are based on a combination of historical results, current forecasts, market data and recent economic events. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2019 and 2018, respectively, goodwill and indefinite-lived trademarks totaled $1.9 billion and $1.8 billion. WESCO performed its annual impairment tests of goodwill and indefinite-lived intangible assets during the fourth quarter. A possible indicator of goodwill impairment is the relationship of a company’s market capitalization to its book value. As of December 31, 2019, WESCO's market capitalization exceeded its book value and the fair values of its reporting units exceeded their carrying values. Accordingly, there were no impairment losses identified as a result of the annual test. The determination of fair value involves significant management judgment and management applies its best judgment when assessing the reasonableness of financial projections. Fair values are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill and indefinite-lived intangible impairment tests will prove to be an accurate prediction of future results.
Definite Lived Intangible Assets	Definite Lived Intangible Assets Definite lived intangible assets are amortized over 2 to 20 years. A portion of definite lived intangible assets related to certain customer relationships are amortized using an accelerated method whereas all other definite lived intangible assets subject to amortization use a straight-line method. In either case, the amortization method reflects the pattern in which the economic benefits of the respective assets are consumed or otherwise used. Definite lived intangible assets are tested for impairment if events or circumstances occur indicating that the respective asset might be impaired.
Insurance Programs	Insurance Programs WESCO uses commercial insurance for auto, workers’ compensation, casualty and health claims, and information technology as a risk-reduction strategy to minimize catastrophic losses. The Company’s strategy involves large deductible policies where WESCO must pay all costs up to the deductible amount. WESCO estimates the reserve for these programs based on historical incident rates and costs. The assumptions included in developing this accrual include the period of time between the incurrence and payment of a claim. The total liability related to insurance programs was $12.9 million and $13.1 million at December 31, 2019 and 2018, respectively.
Income Taxes	Income Taxes WESCO accounts for income taxes under the asset and liability method, which requires the recognition of deferred income taxes for events that have future tax consequences. Under this method, deferred income taxes are recognized (using enacted tax laws and rates) based on the future income tax effects of differences in the carrying amounts of assets and liabilities for financial reporting and tax purposes. The effect of a tax rate change on deferred tax assets and liabilities is recognized in income in the period of change. WESCO recognizes deferred tax assets at amounts that are expected to be realized. To make such determination, management evaluates all positive and negative evidence, including but not limited to, prior, current and future taxable income, tax planning strategies and future reversals of existing temporary differences. A valuation allowance is recognized if it is “more-likely-than-not” that some or all of a deferred tax asset will not be realized. WESCO regularly assesses the realizability of deferred tax assets. WESCO accounts for uncertainty in income taxes using a "more-likely-than-not" recognition threshold. Due to the subjectivity inherent in the evaluation of uncertain tax positions, the tax benefit ultimately recognized may materially differ from the estimate. WESCO recognizes interest and penalties related to uncertain tax benefits as part of interest expense and income tax expense, respectively. The Tax Cuts and Jobs Act of 2017 (the “TCJA”) imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax"). Except for the portion of previously taxed foreign earnings that have been repatriated, WESCO continues to assert that the remaining undistributed earnings of its foreign subsidiaries, the majority of which were subject to the transition tax, are indefinitely reinvested. WESCO believes it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without repatriating cash held by these foreign subsidiaries. Upon any future repatriation, additional tax expense or benefit may be incurred; however, management does not believe it will be material. The provisions of the TCJA also introduced U.S. taxation on certain global intangible low-taxed income ("GILTI"). WESCO has elected to account for GILTI tax as a component of income tax expense. Future adjustments (if any) resulting from additional regulatory guidance regarding the accounting for the income tax effects of TCJA will be recognized as discrete income tax expense or benefit in the period in which guidance is issued.
Foreign Currency	Foreign Currency The local currency is the functional currency for the majority of WESCO’s operations outside the United States. Assets and liabilities of these operations are translated to U.S. dollars at the exchange rate in effect at the end of each period. Income statement accounts are translated at an exchange rate that approximates the average for the period. Translation adjustments arising from the use of differing exchange rates from period to period are included as a component of other comprehensive income (loss) within stockholders’ equity. Gains and losses from foreign currency transactions are included in net income for the period.
Defined Benefit Pension Plan	Defined Benefit Pension Plan Liabilities and expenses for pension benefits are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated cash flows, the expected long-term rate of return on plan assets, and several assumptions relating to the employee workforce (salary increases, retirement age, and mortality).
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company measures the fair value of financial assets and liabilities according to a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value and requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible at the measurement date; Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, and Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to measurements involving significant unobservable inputs (Level 3).
Interest Expense, Policy [Policy Text Block]	Net Interest and Other Net interest and other includes interest expense, interest income, amortization of debt discount and debt issuance costs, the non-service cost components of net periodic benefit cost, and foreign exchange gains and losses from the remeasurement of certain financial instruments.
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which introduces new guidance for the accounting for credit losses on certain financial instruments. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Management has compared its current policy for estimating losses resulting from uncollectible trade accounts receivable to the requirements of the new standard. To support the new standard, management is currently identifying and implementing appropriate changes to the its business processes and controls. The new standard will be adopted in the first quarter of 2020. The adoption of this pronouncement is not expected to have an impact on WESCO's consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which amends the disclosure requirements for recurring and nonrecurring fair value measurements by removing, modifying and adding certain disclosures. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, which amends the disclosure requirements for all employers that sponsor defined benefit pension and other post retirement plans by removing and adding certain disclosures. The amendments in this ASU are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which removes certain exceptions to the general principles of Accounting Standards Codification Topic 740, Income Taxes, and simplifies other aspects of accounting for income taxes. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. Early adoption is permitted in any interim or annual period, with any adjustments reflected as of the beginning of the fiscal year of adoption. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. Other pronouncements issued by the FASB or other authoritative accounting standards groups with future effective dates are either not applicable or are not expected to be significant to WESCO’s financial position, results of operations or cash flows.
Reclassification, Policy [Policy Text Block]	Reclassifications The Consolidated Statements of Cash Flows for the years ended December 31, 2019, 2018 and 2017 include certain reclassifications to previously reported amounts to conform to the current period's presentation.
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	Recently Adopted Accounting Pronouncements Effective January 1, 2019, WESCO adopted Accounting Standards Update (ASU) 2016-02, Leases, and all the related amendments (“Topic 842”), a comprehensive new standard that amended various aspects of existing accounting guidance for leases. The adoption of Topic 842 resulted in the recognition of right-of-use assets and lease liabilities for operating leases of approximately$240 million and$245 million, respectively, in the Consolidated Balance Sheet as of January 1, 2019, most of which relate to real estate. The adoption of Topic 842 did not have a material impact on the Consolidated Statements of Income and Comprehensive Income or Consolidated Statements of Cash Flows for the year ended December 31, 2019. The Company used the optional effective date transition method and therefore did not adjust the prior comparative periods presented herein. There was no cumulative-effect adjustment to beginning retained earnings as a result of using this method. In addition, the Company elected the package of practical expedients that allowed the adoption of Topic 842 without reassessing arrangements that commenced prior to the effective date. Additional qualitative and quantitative information about the Company's leases is disclosed in Note 9.

REVENUE Revenue Reductions (Policies)	12 Months Ended
REVENUE Revenue Reductions (Policies)	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue Recognition, Revenue Reductions [Policy Text Block]	WESCO’s revenues are adjusted for variable consideration, which includes customer volume rebates, returns, and discounts. WESCO measures variable consideration by estimating expected outcomes using analysis and inputs based upon historical data, as well as current and forecasted information. Variable consideration is reviewed by management on a monthly basis and revenue is adjusted accordingly. Variable consideration reduced revenue for the years ended December 31, 2019, 2018 and 2017 by approximately $106.6 million, $107.4 million and $91.1 million, respectively.

REVENUE Shipping and Handling (Policies)	12 Months Ended
REVENUE Shipping and Handling (Policies)	Dec. 31, 2019
Income Statement [Abstract]
Shipping and Handling Cost, Policy [Policy Text Block]	Shipping and handling costs are recognized in net sales when they are billed to the customer. These costs are recognized as a component of selling, general and administrative expenses when WESCO does not bill the customer. WESCO has elected to recognize shipping and handling costs as a fulfillment cost. Shipping and handling costs recorded as a component of selling, general and administrative expenses totaled $71.7 million, $74.1 million and $61.8 million for the years ended December 31, 2019, 2018 and 2017, respectively.

COMMITMENTS AND CONTINGENCIES Guarantee (Policies)	12 Months Ended
COMMITMENTS AND CONTINGENCIES Guarantee (Policies)	Dec. 31, 2019
Guarantees and Product Warranties [Abstract]
Guarantees [Text Block]	In an effort to expand the Company's footprint in the Middle East, WESCO has been doing business since 2009 with WESTEC Supplies General Trading (“WESTEC”), an industrial equipment supplier headquartered in the United Arab Emirates. WESTEC has debt facilities comprised of a $5.8 million term loan and a $1.1 million line of credit to support its working capital requirements and joint sales efforts with WESCO. Due to the nature of WESCO’s arrangement with WESTEC, WESCO has provided a standby letter of credit under its revolving credit facility of up to $7.3 million as security for WESTEC’s debt facilities. As of December 31, 2019, WESTEC had outstanding indebtedness totaling $6.3 million. Management currently believes the estimated fair value of the noncontingent guarantee on the outstanding indebtedness is nominal and therefore a liability has not been recorded as of December 31, 2019.

REVENUE (Tables)

12 Months Ended

Dec. 31, 2019

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue [Table Text Block]

The following tables disaggregate WESCO’s net sales by end market and geography:



	Year Ended December 31,
(In thousands)	2019		2018		2017
Industrial	$	3,000,253	$	2,983,062	$	2,852,357
Construction	2,743,852		2,684,844		2,546,261
Utility	1,347,448		1,303,697		1,181,704
Commercial, Institutional and Government	1,267,364		1,204,998		1,098,699
Total by end market	$	8,358,917	$	8,176,601	$	7,679,021



	Year Ended December 31,
(In thousands)	2019		2018		2017
United States	$	6,234,119	$	6,089,130	$	5,775,988
Canada ⁽¹⁾	1,647,066		1,647,933		1,521,378
Other International ⁽¹⁾	477,732		439,538		381,655
Total by geography	$	8,358,917	$	8,176,601	$	7,679,021

⁽¹⁾

The prior periods has been reclassified to confirm to the current period's presentation.

GOODWILL AND INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Goodwill

The following table sets forth the changes in the carrying value of goodwill:



	Year Ended December 31,
	2019		2018
	(In thousands)
Beginning balance January 1	$	1,722,603	$	1,771,877
Foreign currency exchange rate changes	30,670		(49,274		)
Adjustments to goodwill for acquisitions	5,767		—
Ending balance December 31	$	1,759,040	$	1,722,603

Schedule of Intangible Assets by Major Class

The components of intangible assets are as follows:



		December 31, 2019							December 31, 2018
	Life	Gross Carrying Amount ⁽¹⁾		Accumulated Amortization ⁽¹⁾			Net Carrying Amount		Gross Carrying Amount ⁽¹⁾		Accumulated Amortization ⁽¹⁾			Net Carrying Amount
		(In thousands)
Intangible assets:
Trademarks	Indefinite	$	98,699	$	—		$	98,699	$	96,260	$	—		$	96,260
Trademarks	10-15	24,800		(9,319		)	15,481		25,185		(7,585		)	17,600
Non-compete agreements	5	196		(180		)	16		196		(141		)	55
Customer relationships	10-20	358,341		(201,962		)	156,379		358,620		(180,395		)	178,225
Distribution agreements	10-19	37,371		(25,294		)	12,077		36,984		(22,562		)	14,422
Patents	10	48,310		(43,687		)	4,623		48,310		(38,856		)	9,454
		$	567,717	$	(280,442	)	$	287,275	$	565,555	$	(249,539	)	$	316,016

⁽¹⁾

Excludes the original cost and related accumulated amortization of fully-amortized intangible assets.

Schedule of Expected Amortization Expense

The following table sets forth the estimated amortization expense for intangible assets for the next five years and thereafter:



For the year ending December 31,	(In thousands)
2020	$	34,037
2021	26,387
2022	23,903
2023	23,311
2024	19,863
Thereafter	61,075

ACQUISITIONS (Tables)

12 Months Ended

Dec. 31, 2019

Business Acquisition [Line Items]

Schedule of Business Acquisitions, by Acquisition

The following table sets forth the consideration paid for acquisitions:



	Year Ended December 31,
	2019
	(In thousands)
Fair value of assets acquired	$	35,671
Fair value of liabilities assumed	8,074
Cash paid for acquisitions	$	27,597

PROPERTY, BUILDINGS AND EQUIPMENT (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

The following table sets forth the components of property, buildings and equipment:



	As of December 31,
	2019			2018
	(In thousands)
Buildings and leasehold improvements	$	110,056		$	111,510
Furniture, fixtures and equipment	162,029			186,523
Software costs	127,919			115,631
	400,004			413,664
Accumulated depreciation and amortization	(268,415		)	(291,811		)
	131,589			121,853
Land	24,106			23,996
Construction in progress	25,753			15,029
	$	181,448		$	160,878

LEASES (Tables)

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Lease, Cost [Abstract]

Lease, Cost [Table Text Block]

The following table sets forth the Company's total lease cost, which is recorded as a component of selling, general and administrative expenses, for the period ending:



(In thousands)	December 31, 2019
Operating lease cost	$	73,613
Short-term lease cost	90
Variable lease cost	23,385
Total lease cost	$	97,088

Lessee, Operating Lease, Liability, Maturity [Table Text Block]



	(In thousands)
2020	$	72,946
2021	62,549
2022	48,490
2023	38,209
2024	22,426
Thereafter	32,559
Total undiscounted operating lease payments	277,179
Less: interest	(35,303		)
Total operating lease liabilities	$	241,876

Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]

The following table sets forth the future minimum rental payments for operating leases accounted for in accordance with Accounting Standards Codification Topic 840, Leases, as of December 31, 2018:



Years ending December 31	(In thousands)
2019	$	71,640
2020	59,594
2021	47,264
2022	34,490
2023	24,493
Thereafter	40,302

DEBT (Tables)

12 Months Ended

Dec. 31, 2019

Debt Instrument [Line Items]

Schedule of Debt

The following table sets forth WESCO’s outstanding indebtedness:



	As of December 31,
	2019			2018
	(In thousands)
International lines of credit	$	26,255		$	30,785
Term Loan Facility, less debt discount of $156 in 2018	—			24,594
Accounts Receivable Securitization Facility	415,000			275,000
Revolving Credit Facility	—			51,598
5.375% Senior Notes due 2021	500,000			500,000
5.375% Senior Notes due 2024	350,000			350,000
Capital leases	1,373			1,123
Total debt	1,292,628			1,233,100
Less unamortized debt issuance costs	(8,876		)	(9,575		)
Less short-term debt and current portion of long-term debt	(26,685		)	(56,214		)
Total long-term debt	$	1,257,067		$	1,167,311

Schedule of Maturities of Long-term Debt

The following table sets forth the aggregate principal repayment requirements for all indebtedness for the next five years and thereafter, as of December 31, 2019:



	(In thousands)
2020	$	26,685
2021	500,943
2022	415,000
2023	—
2024	350,000
Thereafter	—
Total payments on debt	$	1,292,628

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense

The following table sets forth the components of the provision (benefit) for income taxes:



	Year Ended December 31,
	2019		2018		2017
			(In thousands)
Current income taxes:
Federal	$	31,695	$	28,464	$	122,170
State	8,616		7,458		2,259
Foreign	6,347		10,611		15,274
Total current income taxes	46,658		46,533		139,703
Deferred income taxes:
Federal	6,774		5,253		(48,060		)
State	1,846		1,967		4,508
Foreign	4,585		1,917		(6,844		)
Total deferred income taxes	13,205		9,137		(50,396		)
Provision for income taxes	$	59,863	$	55,670	$	89,307

Schedule of Income before Income Tax, Domestic and Foreign

The following table sets forth the components of income before income taxes by jurisdiction:



	Year Ended December 31,
	2019		2018		2017
			(In thousands)
United States	$	198,566	$	198,556	$	180,957
Foreign	83,495		82,469		71,483
Income before income taxes	$	282,061	$	281,025	$	252,440

Schedule of Effective Income Tax Rate Reconciliation

The following table sets forth the reconciliation between the federal statutory income tax rate and the effective tax rate:



	Year Ended December 31,
	2019		2018		2017
Federal statutory rate	21.0	%	21.0	%	35.0	%
State income taxes, net of federal income tax benefit	3.1		2.8		1.4
Deemed repatriation of undistributed foreign earnings	(1.3	)	(1.2	)	32.8
Deferred income tax remeasurement	—		(0.3	)	(22.4	)
Tax effect of intercompany financing	(5.5	)	(5.6	)	(10.5	)
Other	3.9		3.1		(0.9	)
Effective tax rate	21.2	%	19.8	%	35.4	%

Schedule of Deferred Tax Assets and Liabilities

The following table sets forth deferred tax assets and liabilities:



	As of December 31,
	2019					2018
				(In thousands)
	Assets			Liabilities		Assets			Liabilities
Accounts receivable	$	3,382		$	—	$	3,657		$	—
Inventories	—			4,580		—			3,315
Depreciation of property, buildings and equipment	—			18,393		—			17,384
Operating leases	61,326			60,670		—			—
Amortization of intangible assets	—			159,573		—			158,795
Employee benefits	20,641			—		20,107			—
Stock-based compensation	13,792			—		12,840			—
Tax loss carryforwards	10,486			—		15,557			—
Foreign tax credit carryforwards	1,247			—		—			—
Other	6,791			3,964		7,927			4,115
Deferred income taxes before valuation allowance	117,665			247,180		60,088			183,609
Valuation allowance	(5,854		)	—		(4,072		)	—
Total deferred income taxes	$	111,811		$	247,180	$	56,016		$	183,609

Summary of Income Tax Examinations



United States — Federal		2015 and forward
United States — Material States		2015 and forward
Canada		2008 and forward

Summary of Income Tax Contingencies

The following table sets forth the reconciliation of gross unrecognized tax benefits:



	As of December 31,
	2019			2018			2017
	(In thousands)
Beginning balance January 1	$	1,293		$	4,348		$	6,181
Reductions for tax positions of prior years	—			—			(155		)
Settlements	(1,290		)	(2,646		)	(1,025		)
Lapse in statute of limitations	—			(287		)	(755		)
Foreign currency exchange rate changes	51			(122		)	102
Ending balance December 31	$	54		$	1,293		$	4,348

EARNINGS PER SHARE (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted



	Year Ended December 31,
	2019		2018		2017
(In thousands, except per share data)
Net income attributable to WESCO International	$	223,426	$	227,343	$	163,460
Weighted-average common shares outstanding used in computing basic earnings per share	43,104		46,722		47,849
Common shares issuable upon exercise of dilutive equity awards	383		477		512
Weighted-average common shares outstanding and common share equivalents used in computing diluted earnings per share	43,487		47,199		48,361
Earnings per share attributable to WESCO International
Basic	$	5.18	$	4.87	$	3.42
Diluted	$	5.14	$	4.82	$	3.38

EMPLOYEE BENEFIT PLANS - (Tables)

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Retirement Benefits [Abstract]

Defined Benefit Plan, Plan Assets, Allocation [Table Text Block]

The asset mix is reviewed and rebalanced to target on an annual basis.



Asset Category	Target %
Canadian equities	12.5	%
Non-Canadian equities	27.5	%
Total equities	40	%
Fixed income investments	45	%
Other investments	15	%

Schedule of Net Funded Status [Table Text Block]

The following tables present the changes in benefit obligations, plan assets and funded status for the defined benefit plans and the components of net periodic pension cost.



	Year Ended December 31,
(In thousands)	2019			2018
Accumulated Benefit Obligation (ABO) at December 31	$	104,649		$	78,746

Change in Projected Benefit Obligation (PBO)
PBO at beginning of year	$	105,515		$	120,319
Service cost	4,602			5,242
Interest cost	4,362			4,137
Participant contributions	736			745
Actuarial loss (gain), including assumption changes	18,591			(11,644		)
Benefits paid	(4,459		)	(3,892		)
Foreign currency exchange rate changes	5,505			(9,392		)
PBO at end of year	$	134,852		$	105,515

Change in Plan Assets
Fair value of plan assets at beginning of year	$	86,556		$	97,182
Actual return on plan assets	12,763			(425		)
Participant contributions	736			745
Employer contributions	3,198			372
Benefits paid	(4,459		)	(3,892		)
Foreign currency exchange rate changes	4,591			(7,426		)
Fair value of plan assets at end of year	$	103,385		$	86,556

Funded Status	$	(31,467	)	$	(18,959	)

Amounts Recognized in the Consolidated Balance Sheets
Other current liabilities	$	(383	)	$	(364	)
Other noncurrent liabilities	(31,084		)	(18,595		)
Net amount recognized	$	(31,467	)	$	(18,959	)

Amounts Recognized in Accumulated Other Comprehensive Income (Loss)
Net actuarial loss (gain)	$	8,890		$	(2,696	)
Total amount recognized, before tax effect	$	8,890		$	(2,696	)

Schedule of Net Benefit Costs [Table Text Block]



	Year Ended December 31,
	2019			2018			2017
	(In thousands)
Components of Net Periodic Pension Cost
Service cost	$	4,602		$	5,242		$	4,328
Interest cost	4,362			4,137			3,912
Expected return on plan assets	(5,695		)	(5,969		)	(5,562		)
Recognized actuarial gain	(63		)	(46		)	(149		)
Net periodic pension cost	$	3,206		$	3,364		$	2,529

Other Changes in Plan Assets and PBO Recognized in Accumulated Other Comprehensive Income (Loss)
Net actuarial loss (gain)	$	11,523		$	(5,250	)	$	8,593
Amortization of unrecognized net actuarial gain	63			46			149
Total amount recognized, before tax effect	11,586			(5,204		)	8,742
Tax effect	(2,943		)	1,406			(2,361		)
Total amount recognized, after tax effect	$	8,643		$	(3,798	)	$	6,381

Total recognized in net periodic pension cost and accumulated other comprehensive income (loss)	$	11,849		$	(434	)	$	8,910

Schedule of Allocation of Plan Assets [Table Text Block]

The Plan's weighted asset allocations by asset category are as follows:



	As of December 31
	2019		2018
Asset Category
Pooled Funds:
Canadian equities	12.5	%	12.4	%
U.S. equities	5.0	%	5.0	%
Non-North American equities	22.5	%	22.5	%
Fixed income investments	44.8	%	44.7	%
Other	15.2	%	15.4	%
Total	100.0	%	100.0	%

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

The following tables set forth the fair value of the Plan's assets by asset category:



	December 31, 2019
(In thousands)	Level 1		Level 2		Level 3		NAV⁽¹⁾		Total
Pooled Funds:
Canadian equities	$	—	$	—	$	—	$	12,973	$	12,973
U.S. equities	—		—		—		5,160		5,160
Non-North American equities	—		—		—		23,239		23,239
Fixed income investments	—		—		—		46,309		46,309
Other	224		—		—		15,480		15,704
Total investments	$	224	$	—	$	—	$	103,161	$	103,385



	December 31, 2018
(In thousands)	Level 1		Level 2		Level 3		NAV⁽¹⁾		Total
Pooled Funds:
Canadian equities	$	—	$	—	$	—	$	10,693	$	10,693
U.S. equities	—		—		—		4,356		4,356
Non-North American equities	—		—		—		19,492		19,492
Fixed income investments	—		—		—		38,668		38,668
Other	203		—		—		13,144		13,347
Total investments	$	203	$	—	$	—	$	86,353	$	86,556

⁽¹⁾

As described above, investments measured at fair value using the NAV per share practical expedient have not been classified in the fair value hierarchy. The amounts presented in the tables are intended to reconcile the fair value hierarchy to the total fair value of plan assets.

Pension and Other Postretirement Plans, Pensions, Policy [Policy Text Block]

14. EMPLOYEE BENEFIT PLANS

Defined Contribution Plans

A majority of WESCO’s employees are covered by defined contribution retirement savings plans for their services rendered subsequent to WESCO’s formation. WESCO also offers a deferred compensation plan for select individuals. For U.S. participants, WESCO matches contributions made by employees at an amount equal to 50% of participants' total monthly contributions up to a maximum of 6% of eligible compensation. For Canadian participants, WESCO makes contributions in amounts ranging from 3% to 5% of participants' eligible compensation based on years of continuous service. WESCO may also make, subject to the Board's approval, a discretionary contribution to the defined contribution retirement savings plan covering U.S. participants if certain predetermined profit levels are attained. There were no discretionary contributions for the year ended December 31, 2019. Discretionary employer contribution charges of $20.6 million and $10.0 million were incurred in 2018 and 2017 respectively. For the years ended December 31, 2019, 2018 and 2017, WESCO incurred charges of $27.1 million, $42.0 million, and $31.3 million, respectively, for all such plans. Contributions are made in cash to employee retirement savings plan accounts. The deferred compensation plan is an unfunded plan. As of December 31, 2019 and 2018, the Company's obligation under the deferred compensation plan was $25.2 million and $21.9 million, respectively. Employees have the option to transfer balances allocated to their accounts in the defined contribution retirement savings plan and the deferred compensation plan into any of the available investment options.

Defined Benefit Plans

The Company sponsors a contributory defined benefit plan (the "Plan") covering substantially all Canadian employees of EECOL. The Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the Plan. Participants become 100% vested after two years of continuous service or, if earlier, at the participant's normal retirement age.

The Company also sponsors a Supplemental Executive Retirement Plan (the "SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the SERP was closed to new participants and existing participants became 100% vested. SERP participants continue to contribute 4% of their earnings to the Plan.

The following tables present the changes in benefit obligations, plan assets and funded status for the defined benefit plans and the components of net periodic pension cost.



	Year Ended December 31,
(In thousands)	2019			2018
Accumulated Benefit Obligation (ABO) at December 31	$	104,649		$	78,746

Change in Projected Benefit Obligation (PBO)
PBO at beginning of year	$	105,515		$	120,319
Service cost	4,602			5,242
Interest cost	4,362			4,137
Participant contributions	736			745
Actuarial loss (gain), including assumption changes	18,591			(11,644		)
Benefits paid	(4,459		)	(3,892		)
Foreign currency exchange rate changes	5,505			(9,392		)
PBO at end of year	$	134,852		$	105,515

Change in Plan Assets
Fair value of plan assets at beginning of year	$	86,556		$	97,182
Actual return on plan assets	12,763			(425		)
Participant contributions	736			745
Employer contributions	3,198			372
Benefits paid	(4,459		)	(3,892		)
Foreign currency exchange rate changes	4,591			(7,426		)
Fair value of plan assets at end of year	$	103,385		$	86,556

Funded Status	$	(31,467	)	$	(18,959	)

Amounts Recognized in the Consolidated Balance Sheets
Other current liabilities	$	(383	)	$	(364	)
Other noncurrent liabilities	(31,084		)	(18,595		)
Net amount recognized	$	(31,467	)	$	(18,959	)

Amounts Recognized in Accumulated Other Comprehensive Income (Loss)
Net actuarial loss (gain)	$	8,890		$	(2,696	)
Total amount recognized, before tax effect	$	8,890		$	(2,696	)



	Year Ended December 31,
	2019			2018			2017
	(In thousands)
Components of Net Periodic Pension Cost
Service cost	$	4,602		$	5,242		$	4,328
Interest cost	4,362			4,137			3,912
Expected return on plan assets	(5,695		)	(5,969		)	(5,562		)
Recognized actuarial gain	(63		)	(46		)	(149		)
Net periodic pension cost	$	3,206		$	3,364		$	2,529

Other Changes in Plan Assets and PBO Recognized in Accumulated Other Comprehensive Income (Loss)
Net actuarial loss (gain)	$	11,523		$	(5,250	)	$	8,593
Amortization of unrecognized net actuarial gain	63			46			149
Total amount recognized, before tax effect	11,586			(5,204		)	8,742
Tax effect	(2,943		)	1,406			(2,361		)
Total amount recognized, after tax effect	$	8,643		$	(3,798	)	$	6,381

Total recognized in net periodic pension cost and accumulated other comprehensive income (loss)	$	11,849		$	(434	)	$	8,910

The service cost of $4.6 million, $5.2 million and $4.3 million for the years ended December 31, 2019, 2018 and 2017, respectively, was reported as a component of selling, general and administrative expenses. The other components of net periodic benefit cost totaling a net benefit of $1.4 million, $1.9 million and $1.8 million for the years ended December 31, 2019, 2018 and 2017, respectively, were presented as a component of net interest and other.

The interest rate used to discount future estimated cash flows is determined using the Canadian Institute of Actuaries ("CIA") methodology, which references yield curve information and matches expected benefit payments. The expected long-term rate of return on plan assets is applied to the fair market-related value of plan assets at the beginning of the year.

The following weighted-average actuarial assumptions were used to determine benefit obligations at December 31:



	2019				2018
	Pension Plan		SERP		Pension Plan		SERP
Discount rate	3.2	%	3.2	%	4.0	%	4.0	%
Rate of compensation increase	3.5	%	3.5	%	3.8	%	3.8	%

The following weighted-average actuarial assumptions were used to determine net periodic pension costs at January 1:



	Year Ended December 31,
	2019				2018				2017
	Pension Plan		SERP		Pension Plan		SERP		Pension Plan		SERP
Discount rate	4.0	%	4.0	%	3.5	%	3.5	%	3.9	%	3.9	%
Expected long-term return on assets	6.4	%	n/a		6.4	%	n/a		6.4	%	n/a
Rate of compensation increase	3.8	%	3.8	%	3.8	%	3.8	%	3.8	%	3.8	%

The following benefit payments, which reflect expected future service, are expected to be paid:



Years ending December 31	(In thousands)
2020	$	3,740
2021	3,862
2022	3,915
2023	4,089
2024	4,166
2025 to 2029	26,159

The Company expects to contribute approximately $3.2 million and $0.4 million to the Plan and SERP, respectively, in 2020.

The Plan's weighted asset allocations by asset category are as follows:



	As of December 31
	2019		2018
Asset Category
Pooled Funds:
Canadian equities	12.5	%	12.4	%
U.S. equities	5.0	%	5.0	%
Non-North American equities	22.5	%	22.5	%
Fixed income investments	44.8	%	44.7	%
Other	15.2	%	15.4	%
Total	100.0	%	100.0	%

The Plan's long-term overall objective is to maintain benefits at their current level without affecting the cost of maintaining the Plan, assuming that the demographic make-up of the group of members remains the same.

The primary investment objective, in support of the overall objective, is to earn the highest rate of return possible for the Plan, while keeping risk at acceptable levels. The long-term return objective of the Plan is to achieve a minimum annualized rate of return in excess of the actuarial requirements. This translates into a required return of 3.0% above inflation, net of investment management fees. The return objective is consistent with the overall investment risk level that the Plan assumes in order to meet the pension obligations of the Plan. To achieve this long term investment objective, the Plan has adopted an asset mix that has a combination of primarily equity and fixed income investments. Risk is controlled by investing in a well-diversified portfolio of asset classes. A benchmark portfolio is established based on the expected returns for each asset class available. The investment of the Plan's assets in accordance with the benchmark portfolio should enable the Plan to not only attain, but also exceed the minimum overall objective.

The following table presents the target asset mix based on market value for each investment category within which the investment managers must invest the Plan's assets. The asset mix is reviewed and rebalanced to target on an annual basis.



Asset Category	Target %
Canadian equities	12.5	%
Non-Canadian equities	27.5	%
Total equities	40	%
Fixed income investments	45	%
Other investments	15	%

The Plan's assets are measured at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities are classified in the fair value hierarchy based on the lowest level of any input that is significant to the measurement of fair value. Investments for which fair value is measured using the net asset value (NAV) per share practical expedient are not classified in the fair value hierarchy. The following describes the valuation methodologies used to measure the fair value of the Plan's assets.

Pooled Equity Investments. These investments consist of the Plan's share of segregated funds that primarily invest in equity securities. The funds are valued at the net asset value of shares held in the underlying funds.

Pooled Fixed Income Investments. These investments consist of the Plan's share of a segregated fund that primarily invests in Canadian issued bonds and debentures and is valued at the net asset value of shares held in the underlying securities.

Other Investments. These investments consist of cash and cash equivalents, a money market fund and diversified growth funds. The diversified growth funds invest in a broad range of asset classes, including equities, bonds, infrastructure, property, commodities and absolute return strategies. These investments are valued at the net asset value of shares held in the underlying funds.

The fair value methods described above may not be indicative of net realizable value or reflective of future fair values. Additionally, while the Company believes the valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date.

The following tables set forth the fair value of the Plan's assets by asset category:



	December 31, 2019
(In thousands)	Level 1		Level 2		Level 3		NAV⁽¹⁾		Total
Pooled Funds:
Canadian equities	$	—	$	—	$	—	$	12,973	$	12,973
U.S. equities	—		—		—		5,160		5,160
Non-North American equities	—		—		—		23,239		23,239
Fixed income investments	—		—		—		46,309		46,309
Other	224		—		—		15,480		15,704
Total investments	$	224	$	—	$	—	$	103,161	$	103,385



	December 31, 2018
(In thousands)	Level 1		Level 2		Level 3		NAV⁽¹⁾		Total
Pooled Funds:
Canadian equities	$	—	$	—	$	—	$	10,693	$	10,693
U.S. equities	—		—		—		4,356		4,356
Non-North American equities	—		—		—		19,492		19,492
Fixed income investments	—		—		—		38,668		38,668
Other	203		—		—		13,144		13,347
Total investments	$	203	$	—	$	—	$	86,353	$	86,556

⁽¹⁾

Defined Benefit Plan, Assumptions [Table Text Block]

The following weighted-average actuarial assumptions were used to determine benefit obligations at December 31:



	2019				2018
	Pension Plan		SERP		Pension Plan		SERP
Discount rate	3.2	%	3.2	%	4.0	%	4.0	%
Rate of compensation increase	3.5	%	3.5	%	3.8	%	3.8	%

The following weighted-average actuarial assumptions were used to determine net periodic pension costs at January 1:



	Year Ended December 31,
	2019				2018				2017
	Pension Plan		SERP		Pension Plan		SERP		Pension Plan		SERP
Discount rate	4.0	%	4.0	%	3.5	%	3.5	%	3.9	%	3.9	%
Expected long-term return on assets	6.4	%	n/a		6.4	%	n/a		6.4	%	n/a
Rate of compensation increase	3.8	%	3.8	%	3.8	%	3.8	%	3.8	%	3.8	%

Schedule of Expected Benefit Payments [Table Text Block]

The following benefit payments, which reflect expected future service, are expected to be paid:



Years ending December 31	(In thousands)
2020	$	3,740
2021	3,862
2022	3,915
2023	4,089
2024	4,166
2025 to 2029	26,159

STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity

The following table sets forth a summary of stock-settled stock appreciation rights and related information for the periods presented:



	Year Ended December 31,
	2019							2018				2017
	Awards		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life	Aggregate Intrinsic Value (In thousands)		Awards		Weighted-Average Exercise Price		Awards		Weighted-Average Exercise Price
Beginning of year	2,351,633		$	59.26				2,238,607		$	57.75	2,439,487		$	52.62
Granted	213,618		54.63					509,046		62.68		455,807		71.21
Exercised	(113,099	)	35.01					(192,700	)	40.74		(495,181	)	42.19
Canceled	(115,103	)	65.27					(203,320	)	68.69		(161,506	)	66.06
End of year	2,337,049		59.72		5.6	$	13,039	2,351,633		59.26		2,238,607		57.75
Exercisable at end of year	1,723,370		$	59.00	4.7	$	12,053	1,453,932		$	57.93	1,331,580		$	56.96

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

The following table sets forth the weighted-average assumptions used to estimate the fair value of stock-settled stock appreciation rights granted during the periods presented:



	Year Ended December 31,
	2019	2018	2017
Stock-settled stock appreciation rights granted	213,618	509,046	455,807
Risk free interest rate	2.5%	2.5%	1.9%
Expected life (in years)	5	5	5
Expected volatility	29%	28%	29%

Schedule of Share-based Compensation, Restricted Stock Units Award Activity

The following table sets forth a summary of performance-based awards and related information for the periods presented:



	Year Ended December 31,
	2019				2018				2017
	Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value
Unvested at beginning of year	138,896		$	59.33	148,508		$	60.23	149,320		$	60.36
Granted	126,874		54.64		44,144		62.80		39,978		76.63
Vested	(25,696	)	42.44		—		—		—		—
Forfeited	(44,769	)	52.11		(53,756	)	64.67		(40,790	)	76.77
Unvested at end of year	195,305		$	60.24	138,896		$	59.33	148,508		$	60.23

The following table sets forth a summary of time-based restricted stock units and related information for the periods presented:



	Year Ended December 31,
	2019				2018				2017
	Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value		Awards		Weighted-Average Fair Value
Unvested at beginning of year	327,798		$	57.87	290,054		$	58.11	257,096		$	57.47
Granted	192,106		54.13		122,062		62.40		100,993		71.33
Vested	(136,777	)	46.52		(64,166	)	67.91		(44,720	)	84.57
Forfeited	(19,398	)	59.62		(20,152	)	58.15		(23,315	)	57.52
Unvested at end of year	363,729		$	60.00	327,798		$	57.87	290,054		$	58.11

Schedule of Share-based Payment Award, Performance-based Awards, Valuation Assumptions [Table Text Block]

The following table sets forth the assumptions used to estimate the fair value of performance shares granted during the periods presented:



	Year ended December 31,
	2019		2018		2017
Grant date share price	$	54.64	$	62.80	$	71.67
WESCO expected volatility	n/a		n/a		29		%
Peer group median volatility	n/a		n/a		24		%
Risk-free interest rate	n/a		n/a		1.5		%
Correlation of peer company returns	n/a		n/a		114		%

SEGMENTS AND RELATED INFORMATION (Tables)

12 Months Ended

Dec. 31, 2019

Segment Reporting [Abstract]

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas

WESCO attributes revenues from external customers to individual countries on the basis of the point of sale. The following table sets forth information about WESCO by geographic area:



	Net Sales Year Ended December 31,												Long-Lived Assets⁽¹⁾ December 31,
	2019				2018				2017				2019		2018		2017
(In thousands)	(In thousands)												(In thousands)
United States	$	6,234,119	75	%	$	6,089,130	75	%	$	5,775,988	75	%	$	315,288	$	106,078	$	95,851
Canada⁽²⁾	1,647,066		20	%	1,647,933		20	%	1,521,378		20	%	95,642		50,877		56,591
Other International⁽²⁾	477,732		5	%	439,538		5	%	381,655		5	%	6,352		3,923		4,003
Total	$	8,358,917			$	8,176,601			$	7,679,021			$	417,282	$	160,878	$	156,445


⁽¹⁾	As described in Note 2, effective January 1, 2019, the Company adopted Topic 842 using the effective date method. The adoption of Topic 842 resulted in the recognition of right-of-use assets in the balance sheet. As of December 31, 2019, long-lived assets include $235.8 million of operating lease assets.

⁽²⁾

The prior period has been reclassified to confirm to the current period presentation.

Revenue from External Customers by Products and Services

The following table sets forth information about WESCO’s sales by product category:



	Year Ended December 31,
	2019	2018	2017
(percentages based on total sales)
General Supplies	41%	40%	40%
Wire, Cable and Conduit	14%	14%	15%
Communications and Security	16%	16%	15%
Electrical Distribution and Controls	10%	11%	10%
Lighting and Sustainability	11%	11%	12%
Automation, Controls and Motors	8%	8%	8%

OTHER FINANCIAL INFORMATION (Tables)

12 Months Ended

Dec. 31, 2019

Condensed Financial Information [Abstract]

Condensed Balance Sheet [Table Text Block]



	Condensed Consolidating Balance Sheet
	December 31, 2018
	(In thousands)
	WESCO International, Inc.		WESCO Distribution, Inc.		Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Cash and cash equivalents	$	—	$	35,931	$	60,412		$	—		$	96,343
Trade accounts receivable, net	—		—		1,166,607			—			1,166,607
Inventories	—		440,422		508,304			—			948,726
Prepaid expenses and other current assets	1,123		57,586		124,523			(9,268		)	173,964
Total current assets	1,123		533,939		1,859,846			(9,268		)	2,385,640
Intercompany receivables, net	—		—		2,403,704			(2,403,704		)	—
Property, buildings and equipment, net	—		63,506		97,372			—			160,878
Intangible assets, net	—		2,131		313,885			—			316,016
Goodwill	—		257,623		1,464,980			—			1,722,603
Investments in affiliates	3,188,124		5,137,783		—			(8,325,907		)	—
Other assets	—		2,905		16,994			—			19,899
Total assets	$	3,189,247	$	5,997,887	$	6,156,781		$	(10,738,879	)	$	4,605,036

Accounts payable	$	—	$	404,373	$	389,975		$	—		$	794,348
Short-term debt	—		—		30,785			—			30,785
Other current liabilities	—		86,600		159,481			(9,268		)	236,813
Total current liabilities	—		490,973		580,241			(9,268		)	1,061,946
Intercompany payables, net	1,053,937		1,349,767		—			(2,403,704		)	—
Long-term debt	—		842,093		325,218			—			1,167,311
Other noncurrent liabilities	—		126,930		119,123			—			246,053
Total WESCO International stockholders’ equity	2,135,310		3,188,124		5,137,783			(8,325,907		)	2,135,310
Noncontrolling interests	—		—		(5,584		)	—			(5,584		)
Total liabilities and stockholders’ equity	$	3,189,247	$	5,997,887	$	6,156,781		$	(10,738,879	)	$	4,605,036

Reclassification

Certain reclassifications have been made to conform the presentation of previously reported amounts to that of the current period.



	Condensed Consolidating Balance Sheet
	December 31, 2019
	(In thousands)
	WESCO International, Inc.		WESCO Distribution, Inc.		Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Cash and cash equivalents	$	—	$	46,499	$	104,403		$	—		$	150,902
Trade accounts receivable, net	—		—		1,187,359			—			1,187,359
Inventories	—		490,071		521,603			—			1,011,674
Prepaid expenses and other current assets	1,124		44,382		144,084			886			190,476
Total current assets	1,124		580,952		1,957,449			886			2,540,411
Intercompany receivables, net	—		—		2,668,314			(2,668,314		)	—
Property, buildings and equipment, net	—		82,753		98,695			—			181,448
Operating lease assets	—		141,824		94,010			—			235,834
Intangible assets, net	—		1,500		285,775			—			287,275
Goodwill	—		257,623		1,501,417			—			1,759,040
Investments in affiliates	3,451,020		5,379,728		—			(8,830,748		)	—
Other assets	—		854		12,773			—			13,627
Total assets	$	3,452,144	$	6,445,234	$	6,618,433		$	(11,498,176	)	$	5,017,635

Accounts payable	$	—	$	402,174	$	428,304		$	—		$	830,478
Short-term debt	—		—		26,255			—			26,255
Other current liabilities	—		42,901		183,539			886			227,326
Total current liabilities	—		445,075		638,098			886			1,084,059
Intercompany payables, net	1,186,661		1,481,653		—			(2,668,314		)	—
Long-term debt	—		842,708		414,359			—			1,257,067
Operating lease liabilities	—		111,291		68,539			—			179,830
Other noncurrent liabilities	—		113,487		124,521			—			238,008
Total WESCO International stockholders’ equity	2,265,483		3,451,020		5,379,728			(8,830,748		)	2,265,483
Noncontrolling interests	—		—		(6,812		)	—			(6,812		)
Total liabilities and stockholders’ equity	$	3,452,144	$	6,445,234	$	6,618,433		$	(11,498,176	)	$	5,017,635

Condensed Income Statement [Table Text Block]



	Condensed Consolidating Statement of Income and Comprehensive Income
	Year ended December 31, 2017
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net sales	$	—		$	3,370,088		$	4,441,655		$	(132,722	)	$	7,679,021
Cost of goods sold (excluding depreciation and	—			2,714,511			3,612,577			(132,722		)	6,194,366
amortization)
Selling, general and administrative expenses	—			555,503			546,095			—			1,101,598
Depreciation and amortization	—			18,442			45,575			—			64,017
Results of affiliates’ operations	160,587			168,782			—			(329,369		)	—
Net interest and other	—			94,313			(27,713		)	—			66,600
Provision for income taxes	(2,546		)	(4,486		)	96,339			—			89,307
Net income	$	163,133		$	160,587		$	168,782		$	(329,369	)	$	163,133
Less: Net loss attributable to noncontrolling interests	—			—			(327		)	—			(327		)
Net income attributable to WESCO International	$	163,133		$	160,587		$	169,109		$	(329,369	)	$	163,460
Other comprehensive income (loss):
Foreign currency translation adjustments	85,762			85,762			85,762			(171,524		)	85,762
Post retirement benefit plan adjustments, net of tax	(6,381		)	(6,381		)	(6,381		)	12,762			(6,381		)
Comprehensive income attributable to WESCO International	$	242,514		$	239,968		$	248,490		$	(488,131	)	$	242,841



	Condensed Consolidating Statement of Income and Comprehensive Income
	Year ended December 31, 2018
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net sales	$	—		$	3,572,406		$	4,757,321		$	(153,126	)	$	8,176,601
Cost of goods sold (excluding depreciation and	—			2,890,490			3,871,856			(153,126		)	6,609,220
amortization)
Selling, general and administrative expenses	—			590,009			561,935			—			1,151,944
Depreciation and amortization	—			18,334			44,663			—			62,997
Results of affiliates’ operations	225,355			209,802			—			(435,157		)	—
Net interest and other	—			54,178			17,237			—			71,415
Provision for income taxes	—			3,842			51,828			—			55,670
Net income	225,355			225,355			209,802			(435,157		)	225,355
Less: Net loss attributable to noncontrolling interests	—			—			(1,988		)	—			(1,988		)
Net income attributable to WESCO International	$	225,355		$	225,355		$	211,790		$	(435,157	)	$	227,343
Other comprehensive income (loss):
Foreign currency translation adjustments	(99,643		)	(99,643		)	(99,643		)	199,286			(99,643		)
Post retirement benefit plan adjustments, net of tax	3,798			3,798			3,798			(7,596		)	3,798
Comprehensive income attributable to WESCO International	$	129,510		$	129,510		$	115,945		$	(243,467	)	$	131,498



	Condensed Consolidating Statement of Income and Comprehensive Income
	Year ended December 31, 2019
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net sales	$	—		$	3,642,413		$	4,899,987		$	(183,483	)	$	8,358,917
Cost of goods sold (excluding depreciation and	—			2,954,246			4,006,693			(183,483		)	6,777,456
amortization)
Selling, general and administrative expenses	—			593,025			580,112			—			1,173,137
Depreciation and amortization	—			19,155			42,952			—			62,107
Results of affiliates’ operations	222,198			201,247			—			(423,445		)	—
Net interest and other	—			49,392			14,764			—			64,156
Provision for income taxes	—			5,644			54,219			—			59,863
Net income	222,198			222,198			201,247			(423,445		)	222,198
Less: Net loss attributable to noncontrolling interests	—			—			(1,228		)	—			(1,228		)
Net income attributable to WESCO International	$	222,198		$	222,198		$	202,475		$	(423,445	)	$	223,426
Other comprehensive income (loss):
Foreign currency translation adjustments	49,306			49,306			49,306			(98,612		)	49,306
Post retirement benefit plan adjustments, net of tax	(8,643		)	(8,643		)	(8,643		)	17,286			(8,643		)
Comprehensive income attributable to WESCO International	$	262,861		$	262,861		$	243,138		$	(504,771	)	$	264,089

Condensed Cash Flow Statement [Table Text Block]



	Condensed Consolidating Statement of Cash Flows
	Year ended December 31, 2017
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net cash (used in) provided by operating activities	$	(36,575	)	$	101,826		$	83,871		$	—		$	149,122
Investing activities:
Capital expenditures	—			(13,215		)	(8,292		)	—			(21,507		)
Proceeds from sale of assets	—			—			6,766			—			6,766
Dividends received from subsidiaries	—			307,784			—			(307,784		)	—
Advances to subsidiaries and other	—			(383,686		)	26,912			366,220			9,446
Net cash (used in) provided by investing activities	—			(89,117		)	25,386			58,436			(5,295		)
Financing activities:
Proceeds from issuance of debt	143,367			775,926			1,144,848			(383,686		)	1,680,455
Repayments of debt	—			(785,392		)	(952,740		)	17,466			(1,720,666		)
Equity activities	(106,792		)	—			—			—			(106,792		)
Dividends paid by subsidiaries	—			—			(307,784		)	307,784			—
Other	—			5,807			—			—			5,807
Net cash provided by (used in) financing activities	36,575			(3,659		)	(115,676		)	(58,436		)	(141,196		)
Effect of exchange rate changes on cash and cash equivalents	—			—			5,191			—			5,191
Net change in cash and cash equivalents	—			9,050			(1,228		)	—			7,822
Cash and cash equivalents at the beginning of period	—			41,552			68,579			—			110,131
Cash and cash equivalents at the end of period	$	—		$	50,602		$	67,351		$	—		$	117,953



	Condensed Consolidating Statement of Cash Flows
	Year ended December 31, 2019
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net cash provided by operating activities	$	20,328		$	188,797		$	15,242		$	—		$	224,367
Investing activities:
Capital expenditures	—			(22,330		)	(21,737		)	—			(44,067		)
Acquisition payments	—			(27,597		)	—			—			(27,597		)
Proceeds from sale of assets	—			—			16,795			—			16,795
Dividends received from subsidiaries	—			134,853			—			(134,853		)	—
Advances to subsidiaries and other	—			(222,482		)	(5,931		)	222,482			(5,931		)
Net cash used in investing activities	—			(137,556		)	(10,873		)	87,629			(60,800		)
Financing activities:
Proceeds from issuance of debt	132,721			423,441			998,019			(222,482		)	1,331,699
Repayments of debt	—			(449,190		)	(824,302		)	—			(1,273,492		)
Equity activities	(153,049		)	—			—			—			(153,049		)
Dividends paid by subsidiaries	—			—			(134,853		)	134,853			—
Other	—			(14,924		)	—			—			(14,924		)
Net cash (used in) provided by financing activities	(20,328		)	(40,673		)	38,864			(87,629		)	(109,766		)
Effect of exchange rate changes on cash and cash equivalents	—			—			758			—			758
Net change in cash and cash equivalents	—			10,568			43,991			—			54,559
Cash and cash equivalents at the beginning of period	—			35,931			60,412			—			96,343
Cash and cash equivalents at the end of period	$	—		$	46,499		$	104,403		$	—		$	150,902



	Condensed Consolidating Statement of Cash Flows
	Year ended December 31, 2018
	(In thousands)
	WESCO International, Inc.			WESCO Distribution, Inc.			Non-Guarantor Subsidiaries			Consolidating and Eliminating Entries			Consolidated
Net cash provided by operating activities	$	18,672		$	153,467		$	124,582		$	—		$	296,721
Investing activities:
Capital expenditures	—			(17,573		)	(18,637		)	—			(36,210		)
Proceeds from sale of assets	—			—			12,461			—			12,461
Dividends received from subsidiaries	—			347,531			—			(347,531		)	—
Advances to subsidiaries and other	—			(406,028		)	196,219			199,416			(10,393		)
Net cash (used in) provided by investing activities	—			(76,070		)	190,043			(148,115		)	(34,142		)
Financing activities:
Proceeds from issuance of debt	108,497			339,606			1,086,673			(199,416		)	1,335,360
Repayments of debt	—			(410,606		)	(1,051,611		)	—			(1,462,217		)
Equity activities	(127,169		)	—			—			—			(127,169		)
Dividends paid by subsidiaries	—			—			(347,531		)	347,531			—
Other	—			(21,068		)	—			—			(21,068		)
Net cash used in financing activities	(18,672		)	(92,068		)	(312,469		)	148,115			(275,094		)
Effect of exchange rate changes on cash and cash equivalents	—			—			(9,095		)	—			(9,095		)
Net change in cash and cash equivalents	—			(14,671		)	(6,939		)	—			(21,610		)
Cash and cash equivalents at the beginning of period	—			50,602			67,351			—			117,953
Cash and cash equivalents at the end of period	$	—		$	35,931		$	60,412		$	—		$	96,343

SELECTED QUARTERLY FINANCIAL DATA (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information



	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
2019
Net Sales	$	1,961,267	$	2,150,088	$	2,148,110	$	2,099,452
Cost of goods sold (excluding depreciation and amortization)	1,578,771		1,741,114		1,747,913		1,709,658
Income from operations	70,726		97,950		93,733		83,808
Income before income taxes	53,606		80,643		80,225		67,587
Net income	41,950		63,215		64,339		52,694
Net income attributable to WESCO International	42,369		63,464		64,495		53,098
Basic earnings per share attributable to WESCO International⁽¹⁾	0.94		1.46		1.53		1.27
Diluted earnings per share attributable to WESCO International⁽²⁾	0.93		1.45		1.52		1.26

2018
Net Sales	$	1,993,915	$	2,103,994	$	2,067,245	$	2,011,447
Cost of goods sold (excluding depreciation and amortization)	1,613,966		1,704,100		1,670,037		1,621,117
Income from operations	73,241		91,183		97,517		90,499
Income before income taxes	53,458		73,442		80,467		73,658
Net income	42,971		57,673		66,645		58,066
Net income attributable to WESCO International	44,421		57,940		66,849		58,133
Basic earnings per share attributable to WESCO International⁽¹⁾	0.94		1.23		1.42		1.27
Diluted earnings per share attributable to WESCO International⁽²⁾	0.93		1.22		1.41		1.26

Schedule II - Valuation and Qualifying Accounts (Tables)

12 Months Ended

Dec. 31, 2018

SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]

Allowance for Doubtful Accounts



	Balance at Beginning		Charged to	Charged to Other			Balance at
	of Period		Expense	Accounts⁽¹⁾	Deductions⁽²⁾		End of Period
Allowance for doubtful accounts	(In thousands)
Year ended December 31, 2019	$	24,468	7,006	52	(6,083	)	$	25,443
Year ended December 31, 2018	21,313		10,854	—	(7,699	)	24,468
Year ended December 31, 2017	22,007		8,466	—	(9,160	)	21,313

_________________________


⁽¹⁾	Represents allowance for doubtful accounts in connection with certain acquisitions and divestitures.

⁽²⁾

Includes a reduction in the allowance for doubtful accounts due to write-off of accounts receivable.

ORGANIZATION (Details)	12 Months Ended
ORGANIZATION (Details)	Dec. 31, 2019 distribution_centers customers countries branches
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Customers (in customers) \| customers	70,000
Full service branches (in branches) \| branches	500
Distribution Centers \| distribution_centers	11
Additional countries (in countries) \| countries	16

ACCOUNTING POLICIES - GENERAL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Dec. 31, 2016
Defined Benefit Plan Disclosure
Operating Lease, Right-of-Use Asset	$ 235,834	$ 0		$ 240,000
Income Taxes Receivable, Current	16,371	24,873
Prepaid Expense and Other Assets, Current	76,076	52,107
Assets, Current	2,540,411	2,385,640
Intangible Assets, Net (Including Goodwill)	$ 1,900,000	1,800,000
Characteristics of Securitizations or Asset-backed Financing Arrangements that are Accounted for as Sale	Under the Receivables Facility, WESCO sells, on a continuous basis, an undivided interest in all domestic accounts receivable to WESCO Receivables, a wholly owned special purpose entity (the “SPE”). The SPE sells, without recourse, a senior undivided interest in the receivables to financial institutions for cash while maintaining a subordinated undivided interest in the receivables, in the form of overcollateralization. Since WESCO maintains control of the transferred receivables, the transfers do not qualify for “sale” treatment. As a result, the transferred receivables remain on the balance sheet, and WESCO recognizes the related secured borrowing. WESCO has agreed to continue servicing the sold receivables for the third-party conduits and financial institutions at market rates; accordingly, no servicing asset or liability has been recorded.
Self Insurance Reserve	$ 12,900	13,100
Accounts Receivable, Allowance for Credit Loss, Current	25,400	24,500
Accounts Receivable, Credit Loss Expense (Reversal)	7,000	10,900	$ 8,500
Inventory Valuation Reserves	30,700	27,600
Inventory Write-down	10,000	9,700	8,800
General and Administrative Costs in Inventory, Amount Incurred	71,200	69,200
Stock-based compensation expense	19,062	16,445	14,809
Goodwill	1,759,040	1,722,603	1,771,877
Assets	5,017,635	4,605,036
Liabilities, Current	1,084,059	1,061,946
Deferred Tax Liabilities, Net, Noncurrent	146,617	143,967
Liabilities	2,758,964	2,475,310
Retained Earnings (Accumulated Deficit)	2,530,429	2,307,462	2,079,697		$ 1,914,757
Accumulated Other Comprehensive Income (Loss), Net of Tax	(367,772)	(408,435)	$ (312,590)		$ (391,971)
Stockholders' Equity Attributable to Parent	2,265,483	2,135,310
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,258,671	2,129,726
Liabilities and Equity	5,017,635	$ 4,605,036
Operating Lease, Liability	$ 241,876			$ 245,000
Pension Plan [Member]
Defined Benefit Plan Disclosure
Discount rate	3.20%	4.00%
Minimum
Defined Benefit Plan Disclosure
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Maximum
Defined Benefit Plan Disclosure
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years

ACCOUNTING POLICIES - PPE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Intangible Assets, Net (Including Goodwill)	$ 1,900,000	$ 1,800,000
Property, buildings and equipment, net	$ 181,448	$ 160,878
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	five to forty years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	three to ten years
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	three to five years
Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, net	$ 88,100

REVENUE (Details) - USD ($) $ in Thousands	12 Months Ended
REVENUE (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 8,358,917	$ 8,176,601	$ 7,679,021
Deferred Revenue	12,300	11,800
Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3,000,253	2,983,062	2,852,357
Construction [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,743,852	2,684,844	2,546,261
Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,347,448	1,303,697	1,181,704
Commercial, Institutional and Government [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,267,364	1,204,998	1,098,699
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	6,234,119	6,089,130	5,775,988
Canada
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,647,066	1,647,933	1,521,378
Non-US [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 477,732	$ 439,538	$ 381,655

REVENUE Service Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
REVENUE Service Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 8,358,917	$ 8,176,601	$ 7,679,021

REVENUE Shipping and Handling (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									$ 8,358,917	$ 8,176,601	$ 7,679,021
Cost of Goods and Services Sold	$ 1,709,658	$ 1,747,913	$ 1,741,114	$ 1,578,771	$ 1,621,117	$ 1,670,037	$ 1,704,100	$ 1,613,966	6,777,456	6,609,220	6,194,366
Shipping and Handling [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									$ 71,700	$ 74,100	$ 61,800

GOODWILL AND INTANGIBLE ASSETS - TEXTUALS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Finite-Lived Intangible Assets, Amortization Expense	$ 35.5	$ 35.9	$ 37.8

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF GOODWILL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning balance January 1	$ 1,722,603	$ 1,771,877
Goodwill, Translation Adjustments	30,670	(49,274)
Ending balance December 31	1,759,040	1,722,603
Goodwill, Acquired During Period	$ 5,767	$ 0

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF INTANGIBLE ASSETS BY MAJOR CLASS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ (280,442)	$ (249,539)
Intangible Assets Gross Excluding Goodwill	567,717	565,555
Intangible Assets, Net (Excluding Goodwill)	287,275	316,016
Trademarks
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	24,800	25,185
Finite-Lived Intangible Assets, Accumulated Amortization	(9,319)	(7,585)
Finite-Lived Intangible Assets, Net	$ 15,481	17,600
Non-compete agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Finite-Lived Intangible Assets, Gross	$ 196	196
Finite-Lived Intangible Assets, Accumulated Amortization	(180)	(141)
Finite-Lived Intangible Assets, Net	16	55
Customer relationships
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	358,341	358,620
Finite-Lived Intangible Assets, Accumulated Amortization	(201,962)	(180,395)
Finite-Lived Intangible Assets, Net	156,379	178,225
Distribution agreements
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	37,371	36,984
Finite-Lived Intangible Assets, Accumulated Amortization	(25,294)	(22,562)
Finite-Lived Intangible Assets, Net	12,077	14,422
Patents
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	48,310	48,310
Finite-Lived Intangible Assets, Accumulated Amortization	(43,687)	(38,856)
Finite-Lived Intangible Assets, Net	$ 4,623	9,454
Finite-Lived Intangible Assets, Useful Life, Minimum	10 years
Trademarks
Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Gross	$ 98,699	$ 96,260
Minimum
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Minimum \| Trademarks
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Minimum \| Customer relationships
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Minimum \| Distribution agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Maximum
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Maximum \| Trademarks
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	15 years
Maximum \| Customer relationships
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Maximum \| Distribution agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	19 years

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF EXPECTED AMORTIZATION EXPENSE (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2014	$ 34,037
2015	26,387
2016	23,903
2017	23,311
2018	19,863
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 61,075

CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS (Details)	12 Months Ended
	Dec. 31, 2019
Supplier Concentration Risk \| Cost of Goods, Total
Concentration Risk [Line Items]
Concentration Risk, Percentage	11.00%

ACQUISITIONS - ACQUISITIONS (Details) $ in Thousands	12 Months Ended
ACQUISITIONS - ACQUISITIONS (Details) $ in Thousands	Dec. 31, 2019 USD ($) branches	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Mar. 05, 2019
Number of Stores \| branches	500
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period	$ 100,000
Goodwill, Acquired During Period	5,767	$ 0
Net loss attributable to noncontrolling interest	(1,228)	$ (1,988)	$ (327)
Payments to Acquire Businesses, Gross	$ 27,597
Noncompete Agreements [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Maximum [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Maximum [Member] \| Trademarks
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	15 years
Maximum [Member] \| Customer Relationships
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Minimum
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Minimum \| Trademarks
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Minimum \| Customer Relationships
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years

ACQUISITIONS - SCHEDULE OF BUSINESS ACQUISTIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 35,671
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	8,074
Cash paid for acquisitions	27,597
Supplemental cash flow disclosure related to acquisitions:
Payments to Acquire Businesses, Net of Cash Acquired	$ 27,597	$ 0	$ 0

ACQUISITIONS - SCHEDULE OF PURCHASE PRICE ALLOCATION (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets Acquired
Goodwill	$ 1,759,040	$ 1,722,603	$ 1,771,877
Total assets acquired	35,671
Liabilities Assumed
Total liabilities assumed	$ 8,074

PROPERTY, BUILDINGS AND EQUIPMENT - SCHEDULE OF PROPERTY, BUILDINGS AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (268,415)	$ (291,811)
Property, buildings and equipment, net	181,448	160,878
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	110,056	111,510
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	162,029	186,523
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	127,919	115,631
Depreciable [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	400,004	413,664
Property, buildings and equipment, net	131,589	121,853
Land
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	24,106	23,996
Construction in progress
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	$ 25,753	$ 15,029

PROPERTY, BUILDINGS AND EQUIPMENT - PROPERTY, BUILDINGS AND EQUIPMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 15.9	$ 17.3	$ 16.3
Capitalized software amortization	10.6	9.8	$ 9.9
Unamortized software cost	29.8	24.2
Capitalized leases	9.7	9.3
Accumulated amortization related to capitalized leases	$ 8.3	$ 8.4

LEASES Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Leased Assets [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	5 years 3 months 18 days
Operating Lease, Right-of-Use Asset	$ 235,834	$ 240,000	$ 0
Operating Lease, Liability, Current	62,046
Operating Lease, Liability, Noncurrent	179,830		$ 0
Operating Lease, Liability	$ 241,876	$ 245,000
Operating Lease, Weighted Average Discount Rate, Percent	4.60%

LEASES Lease, Cost (Details) $ in Thousands	12 Months Ended
LEASES Lease, Cost (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Operating Leased Assets [Line Items]
Operating Lease, Cost	$ 73,613
Short-term Lease, Cost	90
Variable Lease, Cost	23,385
Lease, Cost	97,088
Operating Lease, Payments	75,775
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 60,586

LEASES Lessee, Operating Lease, Liability, Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 72,946
Lessee, Operating Lease, Liability, Payments, Due Year Two	62,549
Lessee, Operating Lease, Liability, Payments, Due Year Three	48,490
Lessee, Operating Lease, Liability, Payments, Due Year Four	38,209
Lessee, Operating Lease, Liability, Payments, Due Year Five	22,426
Lessee, Operating Lease, Liability, Payments, Due after Year Five	32,559
Lessee, Operating Lease, Liability, Payments, Due	277,179
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(35,303)
Operating Lease, Liability	$ 241,876	$ 245,000

LEASES Schedule of Future Minimum Rental Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 71,640
Operating Leases, Future Minimum Payments, Due in Two Years	59,594
Operating Leases, Future Minimum Payments, Due in Three Years	47,264
Operating Leases, Future Minimum Payments, Due in Four Years	34,490
Operating Leases, Future Minimum Payments, Due in Five Years	24,493
Operating Leases, Future Minimum Payments, Due Thereafter	$ 40,302

DEBT - SCHEDULE OF DEBT (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total debt	$ 1,292,628	$ 1,233,100
Debt Issuance Costs, Net	(8,876)	(9,575)
Less current and short-term portion	(26,685)	(56,214)
Total Long-term Debt, Excluding Current Maturities	1,257,067	1,167,311
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt	0	24,594
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	500,000
Long-term debt	500,000	500,000
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	350,000
Long-term debt	$ 350,000	350,000
Accounts receivable securitization facility
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	2.00%
Long-term debt	$ 415,000	275,000
Revolving credit facility
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	1.60%
Long-term debt	$ 0	51,598
Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Long-term debt	26,255	30,785
Capital leases
Debt Instrument [Line Items]
Long-term debt	1,373	$ 1,123
United States \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 700,000
Debt Instrument, Interest Rate, Effective Percentage	1.00%

DEBT - DEBT (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended					24 Months Ended
	Sep. 30, 2024	Jun. 14, 2022	Jun. 14, 2021	Jun. 14, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 15, 2021
Debt Instrument [Line Items]
Characteristics of Securitizations or Asset-backed Financing Arrangements that are Accounted for as Sale					Under the Receivables Facility, WESCO sells, on a continuous basis, an undivided interest in all domestic accounts receivable to WESCO Receivables, a wholly owned special purpose entity (the “SPE”). The SPE sells, without recourse, a senior undivided interest in the receivables to financial institutions for cash while maintaining a subordinated undivided interest in the receivables, in the form of overcollateralization. Since WESCO maintains control of the transferred receivables, the transfers do not qualify for “sale” treatment. As a result, the transferred receivables remain on the balance sheet, and WESCO recognizes the related secured borrowing. WESCO has agreed to continue servicing the sold receivables for the third-party conduits and financial institutions at market rates; accordingly, no servicing asset or liability has been recorded.
Accounts Receivable from Securitization					$ 415,000	$ 275,000
Debt Issuance Costs, Net					$ (8,876)	$ (9,575)
Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate					6.32%	8.78%
Long-term debt					$ 26,255	$ 30,785
Term Loan Facility
Debt Instrument [Line Items]
Debt discount on convertible debentures					$ 0	(156)
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Dec. 15, 2021
Long-term debt					$ 500,000	500,000
Debt Instrument, Interest Rate, Stated Percentage					5.375%
Deferred Finance Costs, Gross					$ 8,400
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed					101.00%
Debt Instrument, Face Amount					$ 500,000
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Jun. 15, 2024
Long-term debt					$ 350,000	350,000
Debt Instrument, Interest Rate, Stated Percentage					5.375%
Deferred Finance Costs, Gross					$ 6,000
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed					101.00%
Debt Instrument, Face Amount					$ 350,000
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date					Dec. 12, 2012
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum					On November 19, 2013, the Borrowers and WESCO International entered into an amendment (the “Term Loan Amendment”) to the Term Loan Agreement. The Term Loan Amendment, among other things, reduced the applicable margin on U.S. term loans by 0.50% and the LIBOR floor applicable to the U.S. sub-facility from 1.00% to 0.75%. The modified pricing terms were effective December 13, 2013.
Debt Instrument, Unused Borrowing Capacity, Amount					$ 300,000
Debt Instrument, Decrease, Repayments					500,000
Long-term debt					$ 0	24,594
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Amendment Description					On September 26, 2019, WESCO Distribution amended its accounts receivable securitization facility (the “Receivables Facility”) pursuant to the terms and conditions of a Ninth Amendment to the Fourth Amended and Restated Receivables Purchase Agreement, dated as of September 26, 2019 (the “Receivables Amendment”), by and among WESCO Receivables Corp. (“WESCO Receivables”), WESCO Distribution, the various purchaser groups from time to time party thereto and PNC Bank, National Association, as Administrator. The Receivables Amendment amended the amended and restated receivables purchase agreement entered into on September 24, 2015 (the “Existing Receivables Purchase Agreement” and as amended by the Receivables Amendment, the “Receivables Purchase Agreement”).
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate					2.00%
Accounts Receivable Eligible for Securitization					$ 809,500	758,300
Long-term debt					$ 415,000	275,000
Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Borrowing Capacity, Description					On September 26, 2019, WESCO International, WESCO Distribution and certain other subsidiaries of the Company entered into a $600 million revolving credit facility (the “Revolving Credit Facility”) as a replacement of its existing revolving credit facility entered into on September 24, 2015. The Revolving Credit Facility contains a letter of credit sub-facility of up to $125 million, pursuant to the terms and conditions of a Third Amended and Restated Credit Agreement, dated as of September 26, 2019 (the “Credit Agreement”). The Revolving Credit Facility contains an accordion feature allowing WESCO Distribution to request increases to the borrowing commitments under the Revolving Credit Facility of up to $200 million in the aggregate, subject to customary conditions.
Debt Instrument, Maturity Date					Sep. 01, 2024
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate					1.60%
Debt Instrument, Increase, Additional Borrowings					$ 715,400	473,100
Debt Instrument, Decrease, Repayments					767,400	433,500
Long-term debt					0	51,598
Line of Credit Facility, Remaining Borrowing Capacity					$ 563,800	515,900
Canada \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End					2.00%
Debt Instrument, Face Amount					$ 150,000
United States \| Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End					1.00%
Debt Instrument, Face Amount					$ 700,000
Minimum \| Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity					$ 2,000
Minimum \| Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.95%
Debt Instrument, Unused Borrowing Capacity, Amount					$ 550,000
Maximum \| Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity					$ 21,000
Maximum \| Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.45%
Debt Instrument, Unused Borrowing Capacity, Amount					$ 600,000
Accordion Feature [Member] \| Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount					200,000
Standby Letters of Credit [Member] \| Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					$ 27,200	$ 28,400
Common Stock
Debt Instrument [Line Items]
Common Stock, Par or Stated Value Per Share					$ 0.01	$ 0.01
London Interbank Offered Rate (LIBOR) [Member] \| Minimum \| Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					1.25%
London Interbank Offered Rate (LIBOR) [Member] \| Maximum \| Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					1.50%
Prime Rate [Member] \| Minimum \| Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.25%
Prime Rate [Member] \| Maximum \| Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					0.50%
Forecast [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed							100.00%
Forecast [Member] \| Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	100.00%	101.344%	102.688%	104.031%
Surety Bond [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					$ 36,100	$ 19,500
Property Lease Guarantee [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					$ 7,800	$ 5,300

DEBT - SCHEDULE OF MATURITIES OF LONG-TERM DEBT (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Debt Disclosure [Abstract]
2020	$ 26,685
2021	500,943
2022	415,000
2023	0
2024	350,000
Thereafter	0
Total payments on debt	$ 1,292,628

CAPITAL STOCK (Details) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	20,000,000	20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock
Class of Stock [Line Items]
Common Stock, Shares Authorized	210,000,000	210,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Class B
Class of Stock [Line Items]
Common Stock, Shares Authorized	20,000,000	20,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01

INCOME TAXES - ADDITIONAL INFORMATION (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Deferred Income Tax Expense (Benefit)		$ 900	$ 56,400
Income Tax Examination, Description	The Company is under examination by tax authorities in the U.S. and Canada and remains subject to examination until the applicable statutes of limitation expire. The statutes of limitation for the material jurisdictions in which the Company files income tax returns remain open as follows:United States — Federal 2015 and forwardUnited States — Material States 2015 and forwardCanada 2008 and forward
Deferred Tax Assets, Operating Loss Carryforwards	$ 10,486	15,557
Unrecognized Tax Benefits	54	1,293	4,348	$ 6,181
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	100	1,300	$ 1,700
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ 100	$ 800
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	35.00%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 3,700	$ 3,400	$ 82,800
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	1,247
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Taxes Payable	36,800	43,200	65,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	1,200	6,400
Deferred Tax Assets, Tax Credit Carryforwards			$ 17,800
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	$ 2,600	$ 3,200
Minimum \| Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2020
Minimum \| State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2022
Maximum [Member] \| Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Maximum [Member] \| State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037

INCOME TAXES - SCHEDULE OF COMPONENTS OF INCOME TAX EXPENSE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		$ 900	$ 56,400
Current taxes
Federal	$ 31,695	28,464	122,170
State	8,616	7,458	2,259
Foreign	6,347	10,611	15,274
Total current	46,658	46,533	139,703
Deferred taxes
Federal	6,774	5,253	(48,060)
State	1,846	1,967	4,508
Foreign	4,585	1,917	(6,844)
Total deferred	13,205	9,137	(50,396)
Income tax expense	$ 59,863	$ 55,670	$ 89,307

INCOME TAXES - SCHEDULE OF INCOME BEFORE INCOME TAX, DOMESTIC AND FOREIGN (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
United States									$ 198,566	$ 198,556	$ 180,957
Foreign									83,495	82,469	71,483
Income before income taxes	$ 67,587	$ 80,225	$ 80,643	$ 53,606	$ 73,658	$ 80,467	$ 73,442	$ 53,458	$ 282,061	$ 281,025	$ 252,440

INCOME TAXES - SCHEDULE OF EFFECTIVE INCOME TAX RATE RECONCILIATION (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		$ 0.9	$ 56.4
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 3.7	$ 3.4	$ 82.8
Federal statutory rate	21.00%	21.00%	35.00%
State taxes, net of federal tax benefit	3.10%	2.80%	1.40%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	(1.30%)	(1.20%)	(32.80%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	0.00%	(0.30%)	(22.40%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent	(5.50%)	(5.60%)	(10.50%)
Other	3.90%	3.10%	(0.90%)
Effective income tax rate	21.20%	19.80%	35.40%

INCOME TAXES - SCHEDULE OF DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	(1.30%)	(1.20%)	(32.80%)
Deferred Income Tax Expense (Benefit)	$ 13,205	$ 9,137	$ (50,396)
Deferred Tax Assets, Net [Abstract]
Accounts receivable	3,382	3,657
Employee benefits	20,641	20,107
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	13,792	12,840
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	1,247
Tax loss carryforwards	10,486	15,557
Other	6,791	7,927
Deferred taxes, Assets	111,811	56,016
Deferred Tax Liabilities, Inventory	4,580	3,315
Deferred Tax Liabilities [Abstract]
Depreciation	18,393	17,384
Deferred Tax Assets, Property, Plant and Equipment	61,326
Deferred Tax Liabilities, Leasing Arrangements	60,670
Amortization of intangible assets	159,573	158,795
Other	3,964	4,115
Deferred Tax Assets, Gross	117,665	60,088
Deferred Tax Liabilities, Gross	247,180	183,609
Deferred Tax Assets, Valuation Allowance	$ (5,854)	(4,072)
Foreign Tax Authority
Deferred Tax Liabilities [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards			$ 17,800
Foreign Tax Authority \| Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2020
Foreign Tax Authority \| Maximum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
State and Local Jurisdiction [Member]
Deferred Tax Assets, Net [Abstract]
Tax loss carryforwards	$ 2,600	$ 3,200
State and Local Jurisdiction [Member] \| Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2022
State and Local Jurisdiction [Member] \| Maximum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037

INCOME TAXES - NOLS (Details) - USD ($) $ in Thousands	12 Months Ended
INCOME TAXES - NOLS (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	$ 10,486	$ 15,557
Canada Revenue Agency [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	7,900	7,200
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	2,600	3,200
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	1,200	6,400
Operating Loss Carryforwards, Valuation Allowance	$ 4,600	$ 4,100
Minimum \| State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2022
Minimum \| Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2020
Maximum \| State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037
Maximum \| Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Chilean Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Valuation Allowance	$ 1,200

INCOME TAXES - SCHEDULE OF INCOME TAX CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 100	$ 1,300	$ 1,700
Unrecognized Tax Benefits, Interest on Income Taxes Expense	(800)	(200)	(100)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance January 1	1,293	4,348	6,181
Reductions for tax positions of prior years	0	0	(155)
Settlements	(1,290)	(2,646)	(1,025)
Lapse in statute of limitations	0	(287)	(755)
Ending balance December 31	54	1,293	4,348
Unrecognized Tax Benefits, Increase Resulting from Foreign Currency Translation	$ 51		$ 102
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation		$ (122)

EARNINGS PER SHARE - SCHEDULE OF EARNINGS PER SHARE, BASIC AND DILUTED (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2014
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock									$ 153,049	$ 127,169	$ 106,792
Stock Repurchase Program, Authorized Amount	$ 400,000				$ 300,000				$ 400,000	$ 300,000	$ 300,000	$ 300,000
Stock Repurchase Program Expiration Date									Dec. 31, 2020		Dec. 31, 2017
Treasury Stock, Shares, Acquired									3,455,584	2,003,446	1,778,537
Net Income	$ 53,098	$ 64,495	$ 63,464	$ 42,369	$ 58,133	$ 66,849	$ 57,940	$ 44,421	$ 223,426	$ 227,343	$ 163,460
Weighted average common shares outstanding used in computing basic earnings per share									43,104,000	46,722,000	47,849,000
Common shares issuable upon exercise of dilutive stock options									383,000	477,000	512,000
Weighted average common shares outstanding and common share equivalents used in computing diluted earnings per share									43,487,000	47,199,000	48,361,000
Earnings Per Share attributable to WESCO International, Inc.
Basic	$ 1.27	$ 1.53	$ 1.46	$ 0.94	$ 1.27	$ 1.42	$ 1.23	$ 0.94	$ 5.18	$ 4.87	$ 3.42
Diluted	$ 1.26	$ 1.52	$ 1.45	$ 0.93	$ 1.26	$ 1.41	$ 1.22	$ 0.93	$ 5.14	$ 4.82	$ 3.38
Treasury Stock, Common [Member]
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock			$ 150,000						$ 275,000	$ 125,000	$ 100,000
Treasury Stock, Common, Shares	5,459,030			365,272					5,459,030
Treasury Stock, Shares, Acquired									3,090,312	2,368,738	1,778,537

EARNINGS PER SHARE - EARNINGS PER SHARE (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Payments for Repurchase of Common Stock		$ 153,049	$ 127,169	$ 106,792
Treasury Stock, Shares, Acquired		3,455,584	2,003,446	1,778,537
Stock Appreciation Rights (SARs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share		1,700,000	1,600,000	1,300,000
Treasury Stock, Common [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Treasury Stock, Common, Shares		5,459,030			365,272
Payments for Repurchase of Common Stock	$ 150,000	$ 275,000	$ 125,000	$ 100,000
Treasury Stock, Shares, Acquired		3,090,312	2,368,738	1,778,537

Textuals (Details) - USD ($) $ in Thousands	12 Months Ended
Textuals (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Service Cost	$ 4,602	$ 5,242	$ 4,328
Defined contribution plan, employer discretionary contribution amount		20,600	10,000
Defined contribution plan, cost recognized	27,100	42,000	31,300
Deferred Compensation Liability, Classified, Noncurrent	$ 25,200	$ 21,900
Defined Benefit Plan, Description	The Company sponsors a contributory defined benefit plan (the "Plan") covering substantially all Canadian employees of EECOL. The Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the Plan. Participants become 100% vested after two years of continuous service or, if earlier, at the participant's normal retirement age.
Defined Benefit Plan, Unfunded Plan	The Company also sponsors a Supplemental Executive Retirement Plan (the "SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the SERP was closed to new participants and existing participants became 100% vested. SERP participants continue to contribute 4% of their earnings to the Plan.
Pension Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.20%	4.00%
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 3,200
Other Nonoperating Gains (Losses)	$ (1,400)	$ (1,900)	$ (1,800)
Supplemental Employee Retirement Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.20%	4.00%
Other Postretirement Benefits Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 400
United States
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	50.00%
Defined contribution plan, maximum annual contribution per employee, percent	6.00%
Canada \| Minimum
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	3.00%
Canada \| Maximum
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	5.00%

EMPLOYEE BENEFIT PLANS Benefit Obligations, Plan Assets, and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Accumulated Benefit Obligation (ABO) at December 31	$ 104,649	$ 78,746
PBO at beginning of year	105,515	120,319
Service cost	4,602	5,242	$ 4,328
Interest cost	4,362	4,137	3,912
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	736	745
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	5,695	5,969	5,562
Defined Benefit Plan, Amortization of Gain (Loss)	63	46	149
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan [Table Text Block]	18,591	(11,644)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	4,459	3,892
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	63	46	149
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	11,586	(5,204)	8,742
PBO at end of year	134,852	105,515	120,319
Plan assets at beginning of year	86,556	97,182
Actual return on plan assets	12,763	(425)
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	736	745
Company contributions	3,198	372
Defined Benefit Plan, Plan Assets, Benefits Paid	4,459	3,892
Plan assets at end of year	103,385	86,556	$ 97,182
Funded status	(31,467)	(18,959)
Current liabilities	(383)	(364)
Non-current liabilities	(31,084)	(18,595)
Net pension liability at end of year	(31,467)	(18,959)
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	8,890	(2,696)
Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss)	5,505	(9,392)
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)	4,591	(7,426)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	$ 8,890	$ (2,696)

EMPLOYEE BENEFIT PLANS Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefit Expense	$ 11,849	$ (434)	$ 8,910
Service cost	4,602	5,242	4,328
Interest cost	4,362	4,137	3,912
Expected return on plan assets	(5,695)	(5,969)	(5,562)
Defined Benefit Plan, Amortization of Gain (Loss)	(63)	(46)	(149)
Total net periodic pension cost	3,206	3,364	2,529
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	11,523	(5,250)	8,593
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	63	46	149
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	11,586	(5,204)	8,742
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	(2,943)	1,406	(2,361)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	$ 8,643	$ (3,798)	$ 6,381

EMPLOYEE BENEFIT PLANS Assumptions (Details)	12 Months Ended
EMPLOYEE BENEFIT PLANS Assumptions (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.80%	3.80%	3.80%
Discount rate	3.20%	4.00%
Average salary increases	3.50%	3.80%
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.80%	3.80%	3.80%
Discount rate	3.20%	4.00%
Average salary increases	3.50%	3.80%

EMPLOYEE BENEFIT PLANS Assumptions 2 (Details)	12 Months Ended
EMPLOYEE BENEFIT PLANS Assumptions 2 (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.20%	4.00%
Discount rate	4.00%	3.50%	3.90%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.40%	6.40%	6.40%
Rate of compensation increase	3.80%	3.80%	3.80%
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.20%	4.00%
Discount rate	4.00%	3.50%	3.90%
Rate of compensation increase	3.80%	3.80%	3.80%

EMPLOYEE BENEFIT PLANS Benefit payments (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Retirement Benefits [Abstract]
2013	$ 3,740
2014	3,862
2015	3,915
2016	4,089
2017	4,166
2018-2023	$ 26,159

EMPLOYEE BENEFIT PLANS Asset allocations (Details)	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure
Equity securities	100.00%	100.00%
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Equity securities	44.80%	44.70%
Other Investments [Member]
Defined Benefit Plan Disclosure
Equity securities	15.20%	15.40%
Canada \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Equity securities	12.50%	12.40%
United States \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Equity securities	5.00%	5.00%
Non-US [Member] \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Equity securities	22.50%	22.50%

EMPLOYEE BENEFIT PLANS Target asset allocation (Details)	12 Months Ended
	Dec. 31, 2019
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	The primary investment objective, in support of the overall objective, is to earn the highest rate of return possible for the Plan, while keeping risk at acceptable levels. The long-term return objective of the Plan is to achieve a minimum annualized rate of return in excess of the actuarial requirements. This translates into a required return of 3.0% above inflation, net of investment management fees. The return objective is consistent with the overall investment risk level that the Plan assumes in order to meet the pension obligations of the Plan. To achieve this long term investment objective, the Plan has adopted an asset mix that has a combination of primarily equity and fixed income investments. Risk is controlled by investing in a well-diversified portfolio of asset classes. A benchmark portfolio is established based on the expected returns for each asset class available. The investment of the Plan's assets in accordance with the benchmark portfolio should enable the Plan to not only attain, but also exceed the minimum overall objective.
Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	40.00%
Fixed Income Funds [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	45.00%
Other Investments [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	15.00%
United States \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	27.50%
Canada \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	12.50%

EMPLOYEE BENEFIT PLANS Fair value plan assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure
Total investments	100.00%	100.00%
Defined Benefit Plan, Plan Assets, Amount	$ 103,385	$ 86,556	$ 97,182
Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	224	203
Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Total investments	44.80%	44.70%
Defined Benefit Plan, Plan Assets, Amount	$ 46,309	$ 38,668
Fixed Income Investments [Member] \| Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Fixed Income Investments [Member] \| Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Fixed Income Investments [Member] \| Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Other Investments [Member]
Defined Benefit Plan Disclosure
Total investments	15.20%	15.40%
Defined Benefit Plan, Plan Assets, Amount	$ 15,704	$ 13,347
Other Investments [Member] \| Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	224	203
Other Investments [Member] \| Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Investments [Member] \| Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Canada \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Total investments	12.50%	12.40%
Defined Benefit Plan, Plan Assets, Amount	$ 12,973	$ 10,693
Canada \| Equity Securities [Member] \| Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Canada \| Equity Securities [Member] \| Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Canada \| Equity Securities [Member] \| Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
United States \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Total investments	5.00%	5.00%
Defined Benefit Plan, Plan Assets, Amount	$ 5,160	$ 4,356
United States \| Equity Securities [Member] \| Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
United States \| Equity Securities [Member] \| Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
United States \| Equity Securities [Member] \| Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Non-US [Member] \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Total investments	22.50%	22.50%
Defined Benefit Plan, Plan Assets, Amount	$ 23,239	$ 19,492
Non-US [Member] \| Equity Securities [Member] \| Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Non-US [Member] \| Equity Securities [Member] \| Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Non-US [Member] \| Equity Securities [Member] \| Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Estimate of Fair Value Measurement [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	103,161	86,353
Estimate of Fair Value Measurement [Member] \| Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	46,309	38,668
Estimate of Fair Value Measurement [Member] \| Other Investments [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	15,480	13,144
Estimate of Fair Value Measurement [Member] \| Canada \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	12,973	10,693
Estimate of Fair Value Measurement [Member] \| United States \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	5,160	4,356
Estimate of Fair Value Measurement [Member] \| Non-US [Member] \| Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 23,239	$ 19,492

STOCK-BASED COMPENSATION - STOCK-BASED COMPENSATION (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase to Number of Shares Authorized to be Issued				1,700,000
Stock-based compensation expense				$ 19,062	$ 16,445	$ 14,809
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value				$ 10,700	8,200	17,200
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				3,400,000
Authorized Shares for Issuance Factor				Under the LTIP, the total number of shares of common stock authorized to be issued will be reduced by 1 share of common stock for every 1 share that is subject to a stock appreciation right granted, and 1.83 shares of common stock for every 1 share that is subject to an award other than a stock appreciation right granted on or after May 31, 2017.
Common Stock, Capital Shares Reserved for Future Issuance				2,600,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 20,700
Share-based Payment Arrangement, Expense, Tax Benefit				$ 2,500	$ 2,000	$ 6,400
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 16.36	$ 18.38	$ 20.52
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number				363,729	327,798	290,054	257,096
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 54.13	$ 62.40	$ 71.33
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 19,100	$ 16,400	$ 14,800
Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 800	$ 6,900	$ 13,000
Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number				17,507

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED COMPENSATION, STOCK OPTIONS AND STOCK APPRECIATION RIGHTS AWARD ACTIVITY (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangements By Share Based Payment Award, Options and Stock Appreciation Rights Outstanding [Roll Forward]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 35.01	$ 40.74	$ 42.19
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	195,305	138,896	148,508	149,320
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 54.64	$ 62.80	$ 76.63
Share Based Compensation Arrangements By Share Based Payment Award, Options and Stock Appreciation Rights Outstanding [Roll Forward]
Stock-settled appreciation rights granted	126,874	44,144	39,978
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 16.36	$ 18.38	$ 20.52
Share Based Compensation Arrangements By Share Based Payment Award, Options and Stock Appreciation Rights Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised	113,099	192,700	495,181
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures	115,103	203,320	161,506
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 65.27	$ 68.69	$ 66.06
Weighted Average Remaining Contractual Term, Outstanding	5 years 7 months 6 days
Weighted Average Remaining Contractual Term, Exercisable	4 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 13,039
Aggregate Intrinsic Value, Exercisable	$ 12,053
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	1,723,370	1,453,932	1,331,580
Stock-settled appreciation rights granted	213,618	509,046	455,807
Share-based Payment Arrangement, Option, Exercise Price Range, Exercisable, Weighted Average Exercise Price	$ 59.00	$ 57.93	$ 56.96
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 59.72	$ 59.26	$ 57.75	$ 52.62
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	2,337,049	2,351,633	2,238,607	2,439,487
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 54.63	$ 62.68	$ 71.21
Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	177,798
Share-based Payment Arrangement, Tranche Two [Member] \| Net Income Growth Rate [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	77,856

STOCK-BASED COMPENSATION - SUMMARY OF RESTRICTED STOCK UNITS AND PERFORMANCE-BASED AWARDS (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	195,305	138,896	148,508	149,320
Granted	126,874	44,144	39,978
Vested in Period	(25,696)	0	0
Unvested, Weighted Average Fair Value	$ 60.24	$ 59.33	$ 60.23	$ 60.36
Granted, Weighted Average Fair Value	54.64	62.80	76.63
Vested in Period, Weighted Average Fair Value	$ 42.44	$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(44,769)	(53,756)	(40,790)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 52.11	$ 64.67	$ 76.77
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	363,729	327,798	290,054	257,096
Granted	192,106	122,062	100,993
Vested in Period	(136,777)	(64,166)	(44,720)
Unvested, Weighted Average Fair Value	$ 60.00	$ 57.87	$ 58.11	$ 57.47
Granted, Weighted Average Fair Value	54.13	62.40	71.33
Vested in Period, Weighted Average Fair Value	$ 46.52	$ 67.91	$ 84.57
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(19,398)	(20,152)	(23,315)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 59.62	$ 58.15	$ 57.52
Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	17,507
Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	177,798
Share-based Payment Arrangement, Tranche Two [Member] \| Net Income Growth Rate [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	77,856
Share-based Payment Arrangement, Tranche Two [Member] \| Earnings Per Share Growth [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	19,797
Share-based Payment Arrangement, Tranche Two [Member] \| Return on Net Assets [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	80,145

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED PAYMENT AWARDS, VALUATION ASSUMPTIONS (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	2.50%	2.50%	1.90%
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-settled appreciation rights granted	213,618	509,046	455,807
Expected life (in years)	5 years	5 years	5 years
Expected volatility	29.00%	28.00%	29.00%
Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	17,507

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED PAYMENT AWARD, PERFORMANCE-BASED AWARDS, VALUATION ASSUMPTIONS (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.50%	2.50%	1.90%
Correlation			114.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date share price	$ 54.64	$ 62.80	$ 71.67
WESCO expected volatility			29.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Weighted Average Volatility Rate			24.00%
Risk-free interest rate			1.50%

SEGMENTS AND RELATED INFORMATION - SEGMENTS AND RELATED INFORMATION (Details)	Dec. 31, 2019 stockkeepingunits products
Segment Reporting [Abstract]
Product stock keeping units (in stock keeping units) \| stockkeepingunits	200,000
Products (in products) \| products	1,000,000

SEGMENTS AND RELATED INFORMATION - SCHEDULE OF REVENUE FROM EXTERNAL CUSTOMERS AND LONG LIVED ASSETS, BY GEOGRAPHICAL AREAS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 8,358,917	$ 8,176,601	$ 7,679,021
Long-Lived Assets	417,282	160,878	156,445
Operating Lease, Right-of-Use Asset	235,834	0		$ 240,000
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	6,234,119	6,089,130	5,775,988
Long-Lived Assets	315,288	106,078	95,851
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,647,066	1,647,933	1,521,378
Long-Lived Assets	95,642	50,877	56,591
Non-US [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	477,732	439,538	381,655
Long-Lived Assets	$ 6,352	$ 3,923	$ 4,003

OTHER FINANCIAL INFORMATION - OTHER FINANCIAL INFORMATION (Details) - Unsecured Debt [Member] $ in Millions	Dec. 31, 2019 USD ($)
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500
2024 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 350

OTHER FINANCIAL INFORMATION - CONDENSED CONSOLIDATED BALANCE SHEETS (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Information
Cash and cash equivalents	$ 150,902		$ 96,343	$ 117,953	$ 110,131
Trade accounts receivable	1,187,359		1,166,607
Inventories, net	1,011,674		948,726
Prepaid Expense and Other Assets, Current	76,076		52,107
Total current assets	2,540,411		2,385,640
Property, building and equipment, net	181,448		160,878
Operating Lease, Right-of-Use Asset	235,834	$ 240,000	0
Intangible assets, net	287,275		316,016
Goodwill and other intangibles, net	1,759,040		1,722,603	1,771,877
Other assets	2,379		3,525
Total assets	5,017,635		4,605,036
Accounts payable	830,478		794,348
Short-term debt	26,255		30,785
Other Liabilities, Current	159,367		105,461
Total current liabilities	1,084,059		1,061,946
Operating Lease, Liability, Noncurrent	179,830		0
Long-term Debt, Excluding Current Maturities	1,257,067		1,167,311
Total WESCO International stockholders' equity	2,258,671		2,129,726
Stockholders' Equity Attributable to Parent	2,265,483		2,135,310
Noncontrolling interest	(6,812)		(5,584)	(3,596)	(3,269)
Total liabilities and stockholders' equity	5,017,635		4,605,036
Parent Company
Condensed Financial Information
Cash and cash equivalents	0		0	0	0
Trade accounts receivable	0		0
Inventories, net	0		0
Prepaid Expense and Other Assets, Current	1,124		1,123
Total current assets	1,124		1,123
Intercompany receivables, net	0		0
Property, building and equipment, net	0		0
Operating Lease, Right-of-Use Asset	0
Intangible assets, net	0		0
Goodwill and other intangibles, net	0		0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	3,451,020		3,188,124
Other assets	0		0
Total assets	3,452,144		3,189,247
Accounts payable	0		0
Short-term debt	0		0
Other Liabilities, Current	0		0
Total current liabilities	0		0
Intercompany payables, net	1,186,661		1,053,937
Operating Lease, Liability, Noncurrent	0
Long-term Debt, Excluding Current Maturities	0		0
Liabilities, Other than Long-term Debt, Noncurrent	0		0
Stockholders' Equity Attributable to Parent	2,265,483		2,135,310
Noncontrolling interest	0		0
Total liabilities and stockholders' equity	3,452,144		3,189,247
Guarantor Subsidiaries
Condensed Financial Information
Cash and cash equivalents	46,499		35,931	50,602	41,552
Trade accounts receivable	0		0
Inventories, net	490,071		440,422
Prepaid Expense and Other Assets, Current	44,382		57,586
Total current assets	580,952		533,939
Intercompany receivables, net	0		0
Property, building and equipment, net	82,753		63,506
Operating Lease, Right-of-Use Asset	141,824
Intangible assets, net	1,500		2,131
Goodwill and other intangibles, net	257,623		257,623
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	5,379,728		5,137,783
Other assets	854		2,905
Total assets	6,445,234		5,997,887
Accounts payable	402,174		404,373
Short-term debt	0		0
Other Liabilities, Current	42,901		86,600
Total current liabilities	445,075		490,973
Intercompany payables, net	1,481,653		1,349,767
Operating Lease, Liability, Noncurrent	111,291
Long-term Debt, Excluding Current Maturities	842,708		842,093
Liabilities, Other than Long-term Debt, Noncurrent	113,487		126,930
Stockholders' Equity Attributable to Parent	3,451,020		3,188,124
Noncontrolling interest	0		0
Total liabilities and stockholders' equity	6,445,234		5,997,887
Non-Guarantor Subsidiaries
Condensed Financial Information
Cash and cash equivalents	104,403		60,412	67,351	68,579
Trade accounts receivable	1,187,359		1,166,607
Inventories, net	521,603		508,304
Prepaid Expense and Other Assets, Current	144,084		124,523
Total current assets	1,957,449		1,859,846
Intercompany receivables, net	2,668,314		2,403,704
Property, building and equipment, net	98,695		97,372
Operating Lease, Right-of-Use Asset	94,010
Intangible assets, net	285,775		313,885
Goodwill and other intangibles, net	1,501,417		1,464,980
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0		0
Other assets	12,773		16,994
Total assets	6,618,433		6,156,781
Accounts payable	428,304		389,975
Short-term debt	26,255		30,785
Other Liabilities, Current	183,539		159,481
Total current liabilities	638,098		580,241
Intercompany payables, net	0		0
Operating Lease, Liability, Noncurrent	68,539
Long-term Debt, Excluding Current Maturities	414,359		325,218
Liabilities, Other than Long-term Debt, Noncurrent	124,521		119,123
Stockholders' Equity Attributable to Parent	5,379,728		5,137,783
Noncontrolling interest	(6,812)		(5,584)
Total liabilities and stockholders' equity	6,618,433		6,156,781
Consolidation, Eliminations [Member]
Condensed Financial Information
Operating Lease, Right-of-Use Asset	0
Operating Lease, Liability, Noncurrent	0
Consolidated Entities [Member]
Condensed Financial Information
Cash and cash equivalents	150,902		96,343	117,953	110,131
Trade accounts receivable	1,187,359		1,166,607
Inventories, net	1,011,674		948,726
Prepaid Expense and Other Assets, Current	190,476		173,964
Total current assets	2,540,411		2,385,640
Intercompany receivables, net	0		0
Property, building and equipment, net	181,448		160,878
Operating Lease, Right-of-Use Asset	235,834
Intangible assets, net	287,275		316,016
Goodwill and other intangibles, net	1,759,040		1,722,603
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0		0
Other assets	13,627		19,899
Total assets	5,017,635		4,605,036
Accounts payable	830,478		794,348
Short-term debt	26,255		30,785
Other Liabilities, Current	227,326		236,813
Total current liabilities	1,084,059		1,061,946
Intercompany payables, net	0		0
Operating Lease, Liability, Noncurrent	179,830
Long-term Debt, Excluding Current Maturities	1,257,067		1,167,311
Liabilities, Other than Long-term Debt, Noncurrent	238,008		246,053
Stockholders' Equity Attributable to Parent	2,265,483		2,135,310
Noncontrolling interest	(6,812)		(5,584)
Total liabilities and stockholders' equity	5,017,635		4,605,036
Consolidation, Eliminations [Member]
Condensed Financial Information
Cash and cash equivalents	0		0	$ 0	$ 0
Trade accounts receivable	0		0
Inventories, net	0		0
Prepaid Expense and Other Assets, Current	886		(9,268)
Total current assets	886		(9,268)
Intercompany receivables, net	(2,668,314)		(2,403,704)
Property, building and equipment, net	0		0
Intangible assets, net	0		0
Goodwill and other intangibles, net	0		0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(8,830,748)		(8,325,907)
Other assets	0		0
Total assets	(11,498,176)		(10,738,879)
Accounts payable	0		0
Short-term debt	0		0
Other Liabilities, Current	886		(9,268)
Total current liabilities	886		(9,268)
Intercompany payables, net	(2,668,314)		(2,403,704)
Long-term Debt, Excluding Current Maturities	0		0
Liabilities, Other than Long-term Debt, Noncurrent	0		0
Stockholders' Equity Attributable to Parent	(8,830,748)		(8,325,907)
Noncontrolling interest	0		0
Total liabilities and stockholders' equity	$ (11,498,176)		$ (10,738,879)

OTHER FINANCIAL INFORMATION - CONDENSED CONSOLIDATED INCOME STATEMENT (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Information
Revenues	$ 2,099,452	$ 2,148,110	$ 2,150,088	$ 1,961,267	$ 2,011,447	$ 2,067,245	$ 2,103,994	$ 1,993,915	$ 8,358,917	$ 8,176,601	$ 7,679,021
Cost of goods sold	1,709,658	1,747,913	1,741,114	1,578,771	1,621,117	1,670,037	1,704,100	1,613,966	6,777,456	6,609,220	6,194,366
Selling, General and Administrative Expense									(1,173,137)	(1,151,944)	(1,101,598)
Depreciation, Depletion and Amortization, Nonproduction									(62,107)	(62,997)	(64,017)
Income tax expense									59,863	55,670	89,307
Net income	52,694	64,339	63,215	41,950	58,066	66,645	57,673	42,971	222,198	225,355	163,133
Net Income (Loss) Attributable to Noncontrolling Interest									(1,228)	(1,988)	(327)
Net Income	$ 53,098	$ 64,495	$ 63,464	$ 42,369	$ 58,133	$ 66,849	$ 57,940	$ 44,421	223,426	227,343	163,460
Foreign currency translation adjustment									49,306	(99,643)	85,762
Benefit plan adjustments									(8,643)	3,798	(6,381)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									264,089	131,498	242,841
Parent Company
Condensed Financial Information
Revenues									0	0	0
Cost of goods sold									0	0	0
Selling, General and Administrative Expense									0	0	0
Depreciation, Depletion and Amortization, Nonproduction									0	0	0
Income (Loss) from Subsidiaries, before Tax									222,198	225,355	160,587
Interest Income (Expense), Net											0
Other Nonoperating Income (Expense)									0	0
Income tax expense									0	0	(2,546)
Net income									222,198	225,355	163,133
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income									222,198	225,355	163,133
Foreign currency translation adjustment									49,306	(99,643)	85,762
Benefit plan adjustments									(8,643)	3,798	(6,381)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									262,861	129,510	242,514
Guarantor Subsidiaries
Condensed Financial Information
Revenues									3,642,413	3,572,406	3,370,088
Cost of goods sold									2,954,246	2,890,490	2,714,511
Selling, General and Administrative Expense									(593,025)	(590,009)	(555,503)
Depreciation, Depletion and Amortization, Nonproduction									(19,155)	(18,334)	(18,442)
Income (Loss) from Subsidiaries, before Tax									201,247	209,802	168,782
Interest Income (Expense), Net											(94,313)
Other Nonoperating Income (Expense)									(49,392)	(54,178)
Income tax expense									5,644	3,842	(4,486)
Net income									222,198	225,355	160,587
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income									222,198	225,355	160,587
Foreign currency translation adjustment									49,306	(99,643)	85,762
Benefit plan adjustments									(8,643)	3,798	(6,381)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									262,861	129,510	239,968
Non-Guarantor Subsidiaries
Condensed Financial Information
Revenues									4,899,987	4,757,321	4,441,655
Cost of goods sold									4,006,693	3,871,856	3,612,577
Selling, General and Administrative Expense									(580,112)	(561,935)	(546,095)
Depreciation, Depletion and Amortization, Nonproduction									(42,952)	(44,663)	(45,575)
Income (Loss) from Subsidiaries, before Tax									0	0	0
Interest Income (Expense), Net											27,713
Other Nonoperating Income (Expense)									(14,764)	(17,237)
Income tax expense									54,219	51,828	96,339
Net income									201,247	209,802	168,782
Net Income (Loss) Attributable to Noncontrolling Interest									(1,228)	(1,988)	(327)
Net Income									202,475	211,790	169,109
Foreign currency translation adjustment									49,306	(99,643)	85,762
Benefit plan adjustments									(8,643)	3,798	(6,381)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									243,138	115,945	248,490
Consolidated Entities [Member]
Condensed Financial Information
Revenues									8,358,917	8,176,601	7,679,021
Cost of goods sold									6,777,456	6,609,220	6,194,366
Selling, General and Administrative Expense									(1,173,137)	(1,151,944)	(1,101,598)
Depreciation, Depletion and Amortization, Nonproduction									(62,107)	(62,997)	(64,017)
Income (Loss) from Subsidiaries, before Tax									0	0	0
Interest Income (Expense), Net											(66,600)
Other Nonoperating Income (Expense)									(64,156)	(71,415)
Income tax expense									59,863	55,670	89,307
Net income									222,198	225,355	163,133
Net Income (Loss) Attributable to Noncontrolling Interest									(1,228)	(1,988)	(327)
Net Income									223,426	227,343	163,460
Foreign currency translation adjustment									49,306	(99,643)	85,762
Benefit plan adjustments									(8,643)	3,798	(6,381)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									264,089	131,498	242,841
Consolidation, Eliminations [Member]
Condensed Financial Information
Revenues									(183,483)	(153,126)	(132,722)
Cost of goods sold									(183,483)	(153,126)	(132,722)
Selling, General and Administrative Expense									0	0	0
Depreciation, Depletion and Amortization, Nonproduction									0	0	0
Income (Loss) from Subsidiaries, before Tax									(423,445)	(435,157)	(329,369)
Interest Income (Expense), Net											0
Other Nonoperating Income (Expense)									0	0
Income tax expense									0	0	0
Net income									(423,445)	(435,157)	(329,369)
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income									(423,445)	(435,157)	(329,369)
Foreign currency translation adjustment									(98,612)	199,286	(171,524)
Benefit plan adjustments									17,286	(7,596)	12,762
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(504,771)	(243,467)	(488,131)
Pension Plan [Member]
Condensed Financial Information
Other Nonoperating Gains (Losses)									$ (1,400)	$ (1,900)	$ (1,800)

OTHER FINANCIAL INFORMATION - CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Information
Net cash (used) provided by operating activities	$ 224,367	$ 296,721	$ 149,122
Investing Activities:
Capital expenditures	(44,067)	(36,210)	(21,507)
Payments to Acquire Businesses, Gross	(27,597)
Payments to Acquire Businesses, Net of Cash Acquired	(27,597)	0	0
Proceeds from sale of assets	16,795	12,461	6,766
Advances to subsidiaries and other	(5,931)	(10,393)	9,446
Net cash used in investing activities	(60,800)	(34,142)	(5,295)
Financing Activities:
Other	(3,727)	(1,211)	(2,392)
Net cash provided (used) by financing activities	(109,766)	(275,094)	(141,196)
Effect of exchange rate changes on cash and cash equivalents	758	(9,095)	5,191
Net change in cash and cash equivalents	54,559	(21,610)	7,822
Cash and cash equivalents at the beginning of period	96,343	117,953	110,131
Cash and cash equivalents at the end of period	150,902	96,343	117,953
Parent Company
Condensed Financial Information
Net cash (used) provided by operating activities	20,328	18,672	(36,575)
Investing Activities:
Capital expenditures	0	0	0
Payments to Acquire Businesses, Gross	0
Proceeds from sale of assets	0	0	0
Proceeds from Dividends Received	0	0	0
Payments for Advance to Affiliate	0	0	0
Net cash used in investing activities	0	0	0
Financing Activities:
Proceeds from Issuance of Debt	132,721	108,497	143,367
Repayments of Debt	0	0	0
Equity transactions	(153,049)	(127,169)	(106,792)
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	0	0	0
Other	0	0	0
Net cash provided (used) by financing activities	(20,328)	(18,672)	36,575
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net change in cash and cash equivalents	0	0	0
Cash and cash equivalents at the beginning of period	0	0	0
Cash and cash equivalents at the end of period	0	0	0
Guarantor Subsidiaries
Condensed Financial Information
Net cash (used) provided by operating activities	188,797	153,467	101,826
Investing Activities:
Capital expenditures	(22,330)	(17,573)	(13,215)
Payments to Acquire Businesses, Gross	(27,597)
Proceeds from sale of assets	0	0	0
Proceeds from Dividends Received	134,853	347,531	307,784
Payments for Advance to Affiliate	222,482	406,028	383,686
Net cash used in investing activities	(137,556)	(76,070)	(89,117)
Financing Activities:
Proceeds from Issuance of Debt	423,441	339,606	775,926
Repayments of Debt	(449,190)	(410,606)	(785,392)
Equity transactions	0	0	0
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	0	0	0
Other	(14,924)	(21,068)	5,807
Net cash provided (used) by financing activities	(40,673)	(92,068)	(3,659)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net change in cash and cash equivalents	10,568	(14,671)	9,050
Cash and cash equivalents at the beginning of period	35,931	50,602	41,552
Cash and cash equivalents at the end of period	46,499	35,931	50,602
Non-Guarantor Subsidiaries
Condensed Financial Information
Net cash (used) provided by operating activities	15,242	124,582	83,871
Investing Activities:
Capital expenditures	(21,737)	(18,637)	(8,292)
Payments to Acquire Businesses, Gross	0
Proceeds from sale of assets	16,795	12,461	6,766
Proceeds from Dividends Received	0	0	0
Payments for Advance to Affiliate	5,931	(196,219)	(26,912)
Net cash used in investing activities	(10,873)	190,043	25,386
Financing Activities:
Proceeds from Issuance of Debt	998,019	1,086,673	1,144,848
Repayments of Debt	(824,302)	(1,051,611)	(952,740)
Equity transactions	0	0	0
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	(134,853)	(347,531)	(307,784)
Other	0	0	0
Net cash provided (used) by financing activities	38,864	(312,469)	(115,676)
Effect of exchange rate changes on cash and cash equivalents	758	(9,095)	5,191
Net change in cash and cash equivalents	43,991	(6,939)	(1,228)
Cash and cash equivalents at the beginning of period	60,412	67,351	68,579
Cash and cash equivalents at the end of period	104,403	60,412	67,351
Consolidated Entities [Member]
Condensed Financial Information
Net cash (used) provided by operating activities	224,367	296,721	149,122
Investing Activities:
Capital expenditures	(44,067)	(36,210)	(21,507)
Payments to Acquire Businesses, Gross	(27,597)
Proceeds from sale of assets	16,795	12,461	6,766
Proceeds from Dividends Received	0	0	0
Payments for Advance to Affiliate	5,931	10,393	(9,446)
Net cash used in investing activities	(60,800)	(34,142)	(5,295)
Financing Activities:
Proceeds from Issuance of Debt	1,331,699	1,335,360	1,680,455
Repayments of Debt	(1,273,492)	(1,462,217)	(1,720,666)
Equity transactions	(153,049)	(127,169)	(106,792)
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	0	0	0
Other	(14,924)	(21,068)	5,807
Net cash provided (used) by financing activities	(109,766)	(275,094)	(141,196)
Effect of exchange rate changes on cash and cash equivalents	758	(9,095)	5,191
Net change in cash and cash equivalents	54,559	(21,610)	7,822
Cash and cash equivalents at the beginning of period	96,343	117,953	110,131
Cash and cash equivalents at the end of period	150,902	96,343	117,953
Consolidation, Eliminations [Member]
Condensed Financial Information
Net cash (used) provided by operating activities	0	0	0
Investing Activities:
Capital expenditures	0	0	0
Payments to Acquire Businesses, Gross	0
Proceeds from sale of assets	0	0	0
Proceeds from Dividends Received	(134,853)	(347,531)	(307,784)
Payments for Advance to Affiliate	(222,482)	(199,416)	(366,220)
Net cash used in investing activities	87,629	(148,115)	58,436
Financing Activities:
Proceeds from Issuance of Debt	(222,482)	(199,416)	(383,686)
Repayments of Debt	0	0	17,466
Equity transactions	0	0	0
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	134,853	347,531	307,784
Other	0	0	0
Net cash provided (used) by financing activities	(87,629)	148,115	(58,436)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net change in cash and cash equivalents	0	0	0
Cash and cash equivalents at the beginning of period	0	0	0
Cash and cash equivalents at the end of period	$ 0	$ 0	$ 0

SELECTED QUARTERLY FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 2,099,452	$ 2,148,110	$ 2,150,088	$ 1,961,267	$ 2,011,447	$ 2,067,245	$ 2,103,994	$ 1,993,915	$ 8,358,917	$ 8,176,601	$ 7,679,021
Cost of goods sold	1,709,658	1,747,913	1,741,114	1,578,771	1,621,117	1,670,037	1,704,100	1,613,966	6,777,456	6,609,220	6,194,366
Income from operations	83,808	93,733	97,950	70,726	90,499	97,517	91,183	73,241	346,217	352,440	319,040
Income before income taxes	67,587	80,225	80,643	53,606	73,658	80,467	73,442	53,458	282,061	281,025	252,440
Net income	52,694	64,339	63,215	41,950	58,066	66,645	57,673	42,971	222,198	225,355	163,133
Net Income attributable to WESCO International, Inc.	$ 53,098	$ 64,495	$ 63,464	$ 42,369	$ 58,133	$ 66,849	$ 57,940	$ 44,421	$ 223,426	$ 227,343	$ 163,460
Basic earnings per share attributable to WESCO International, Inc.	$ 1.27	$ 1.53	$ 1.46	$ 0.94	$ 1.27	$ 1.42	$ 1.23	$ 0.94	$ 5.18	$ 4.87	$ 3.42
Diluted earnings per share attributable to WESCO International, Inc.	$ 1.26	$ 1.52	$ 1.45	$ 0.93	$ 1.26	$ 1.41	$ 1.22	$ 0.93	$ 5.14	$ 4.82	$ 3.38

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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