WESCO International (WCC) 10-K 1 Mar 21 2020 FY Annual report Financial data

COVER PAGE

COVER PAGE - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Feb. 25, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-14989
Entity Registrant Name	WESCO International, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	25-1723342
Entity Address, Postal Zip Code	15219
Entity Address, Address Line One	225 West Station Square DriveSuite 700
Entity Address, State or Province	PA
Entity Address, City or Town	Pittsburgh,
City Area Code	412
Local Phone Number	454-2200
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 1.7
Entity Common Stock, Shares Outstanding		50,161,831
Entity Central Index Key	0000929008
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Class A [Member]
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $.01 per share
Trading Symbol	WCC
Name of Exchange	NYSE
Series A Preferred Stock
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing a 1/100th interest in a share of Series A Fixed-Rate Reset Cumulative Perpetual Preferred Stock
Trading Symbol	WCC PR A
Name of Exchange	NYSE
Preferred Share Purchase Right [Member]
Document Information [Line Items]
Title of 12(b) Security	Preferred Share Purchase Rights
Trading Symbol	N/A
Name of Exchange	NYSE

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020		Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 449,135		$ 150,902
Trade accounts receivable, net of allowance for expected credit losses	2,466,903		1,187,359
Other accounts receivable	239,199		98,029
Inventories	2,163,831		1,011,674
Prepaid expenses and other current assets	187,910		92,447
Total current assets	5,506,978		2,540,411
Property, buildings and equipment, net	399,157	[1]	181,448
Operating Lease, Right-of-Use Asset	534,705	[2]	235,834
Intangible assets, net	2,065,495		287,275
Goodwill	3,187,169		1,759,040
Deferred Income Taxes	37,696		11,248
Other assets	93,941		2,379
Assets Held-for-sale	55,073		0
Total assets	11,880,214		5,017,635
Current Liabilities:
Accounts payable	1,707,329		830,478
Accrued payroll and benefit costs	198,535		49,508
Short-term debt and current portion of long-term debt	528,830		26,685
Other current liabilities	552,301		177,388
Total current liabilities	2,986,995		1,084,059
Long-term Debt, Excluding Current Maturities	4,369,953		1,257,067
Operating Lease, Liability, Noncurrent	414,889	[2]	179,830
Deferred Income Tax Liabilities, Net	488,261		146,617
Other noncurrent liabilities	278,010		91,391
Liabilities Held for Sale	5,717		0
Total liabilities	8,543,825		2,758,964
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	0		0
Additional capital	1,942,810		1,039,347
Retained earnings	2,601,662		2,530,429
Treasury stock, at cost	(938,335)		(937,157)
Accumulated other comprehensive income (loss)	(263,134)		(367,772)
Total stockholders' equity	3,343,722		2,265,483
Noncontrolling interest	(7,333)		(6,812)
Total WESCO International stockholders' equity	3,336,389		2,258,671
Total liabilities and stockholders' equity	11,880,214		5,017,635
Common Stock
Stockholders' Equity:
Common Stock	676		593
Common Class B
Stockholders' Equity:
Common Stock	43		43
Preferred Stock
Stockholders' Equity:
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	0		0
Series A Preferred Stock
Stockholders' Equity:
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	$ 0		$ 0
[1]	The components of property, buildings and equipment as of December 31, 2020 exclude a total of $0.3 million that is classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale".
[2]	Operating lease assets and liabilities of $1.9 million and $2.1 million, respectively, are classified as held for sale as of December 31, 2020, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts Receivable, Allowance for Credit Loss	$ 23,909	$ 25,443
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 87,142	$ 8,876
Preferred stock, par value	$ 0.01
Preferred stock, shares authorized	20,000,000
Preferred stock, shares issued	21,612	0
Treasury stock, shares outstanding	21,870,961	21,850,356
Senior Notes [Member]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 1,039
Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	210,000,000	210,000,000
Common stock, shares issued	67,596,515	59,308,018
Common stock, shares outstanding	50,064,985	41,797,093
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
Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares outstanding	0	0
Series A Preferred Stock
Preferred stock, par value	$ 0.01
Preferred stock, shares authorized	25,000
Preferred stock, shares issued	21,612

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net sales	$ 12,325,995	$ 8,358,917	$ 8,176,601
Cost of goods sold (excluding depreciation and amortization below)	9,998,329	6,777,456	6,609,220
Selling, general and administrative expense	1,859,028	1,173,137	1,151,944
Depreciation and amortization	121,600	62,107	62,997
Income from operations	347,038	346,217	352,440
Interest expense, net	226,591	65,710	68,661
Other, net	(2,395)	(1,554)	2,754
Income before income taxes	122,842	282,061	281,025
Provision for income taxes	22,803	59,863	55,670
Net income	100,039	222,198	225,355
Net loss attributable to noncontrolling interest	(521)	(1,228)	(1,988)
Net Income attributable to WESCO International, Inc.	100,560	223,426	227,343
Preferred Stock Dividends, Income Statement Impact	30,139	0	0
Net Income (Loss) Available to Common Stockholders, Basic	70,421	223,426	227,343
Comprehensive Income:
Foreign currency translation adjustment	95,577	49,306	(99,643)
Benefit plan adjustments	9,061	(8,643)	3,798
Comprehensive income attributable to WESCO International, Inc.	$ 175,059	$ 264,089	$ 131,498
Earnings per share :
Basic	$ 1.53	$ 5.18	$ 4.87
Diluted	$ 1.51	$ 5.14	$ 4.82

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Additional Capital	Retained Earnings (Deficit)	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest	Common Stock	Common Class B	Series A Preferred Stock
Common Stock							$ 591	$ 43
Common stock, shares issued							59,045,762	4,339,431
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	$ 0
Preferred stock, shares issued	0
Additional capital	$ 999,156
Retained earnings	2,079,697
Treasury stock, at cost	$ (647,158)
Treasury Stock, Shares	(16,375,653)
Noncontrolling interest	$ (3,596)
Accumulated other comprehensive income (loss)	(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
APIC, Share-based Payment Arrangement, Recognition and Exercise	(45)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	10,790
Treasury Stock, Value, Acquired, Par Value Method		$ (14,981)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation		(1,254)	$ 422				$ 0
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation							18,437
Net Income attributable to WESCO International, Inc.	227,343
Translation adjustment					$ (99,643)
Benefit plan adjustments, tax	1,404
Benefit plan adjustments, net of tax	(3,798)				3,798
Net loss attributable to noncontrolling interest	(1,988)					$ (1,988)
Treasury Stock, Value, Acquired, Cost Method	$ (110,019)
Treasury Stock, Shares, Acquired	(2,003,446)
Common Stock							$ 592	$ 43
Common stock, shares issued							59,157,696	4,339,431
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	$ 0
Preferred stock, shares issued	0
Additional capital	$ 993,666
Retained earnings	2,307,462
Treasury stock, at cost	$ (758,018)
Treasury Stock, Shares	(18,391,042)
Noncontrolling interest	$ (5,584)
Accumulated other comprehensive income (loss)	(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
APIC, Share-based Payment Arrangement, Recognition and Exercise	(84)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	19,062
Treasury Stock, Value, Acquired, Par Value Method		28,901
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation		(2,198)	(459)				$ 0
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation							48,663
Net Income attributable to WESCO International, Inc.	223,426
Translation adjustment					49,306
Benefit plan adjustments, tax	(2,943)
Benefit plan adjustments, net of tax	8,643				(8,643)
Net loss attributable to noncontrolling interest	(1,228)					(1,228)
Treasury Stock, Value, Acquired, Cost Method	$ (178,901)
Treasury Stock, Shares, Acquired	(3,455,584)
Common Stock							$ 593	$ 43
Common stock, shares issued							59,308,018	4,339,431
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	$ 0								$ 0
Preferred stock, shares issued	0
Additional capital	$ 1,039,347
Retained earnings	2,530,429
Treasury stock, at cost	$ (937,157)
Treasury Stock, Shares	(21,850,356)
Noncontrolling interest	$ (6,812)
Accumulated other comprehensive income (loss)	(367,772)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (1,178)			$ 1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				20,605			171,517
Stock Issued During Period, Value, Acquisitions		886,601					$ 82		$ 0
APIC, Share-based Payment Arrangement, Recognition and Exercise	(40)
Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture	19,279
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation		$ (2,377)	$ 812				$ 0
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation							33,248
Stock Issued During Period, Shares, Acquisitions							8,150,228		21,612
Net Income attributable to WESCO International, Inc.	100,560
Dividends, Preferred Stock	(30,139)
Translation adjustment					95,577
Benefit plan adjustments, tax	2,891
Benefit plan adjustments, net of tax	(9,061)				$ 9,061
Net loss attributable to noncontrolling interest	(521)					$ (521)
Common Stock							$ 676	$ 43
Common stock, shares issued							67,596,515	4,339,431
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	$ 0								$ 0
Preferred stock, shares issued	21,612								21,612
Additional capital	$ 1,942,810
Retained earnings	2,601,662
Treasury stock, at cost	$ (938,335)
Treasury Stock, Shares	(21,870,961)
Noncontrolling interest	$ (7,333)
Accumulated other comprehensive income (loss)	$ (263,134)

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity Parenthetical [Abstract]
Benefit plan adjustments, tax	$ 2,891	$ (2,943)	$ 1,404

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net income	$ 100,039	$ 222,198	$ 225,355
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	121,600	62,107	62,997
Stock-based compensation expense	19,279	19,062	16,445
Other operating activities, net	6,366	(11,175)	(3,652)
Deferred income taxes	(33,538)	13,205	9,137
Changes in assets and liabilities
Increase (Decrease) in Accounts Receivable	47,879	11,453	(22,934)
Inventories	203,827	(47,297)	(8,702)
Increase (Decrease) in Other Operating Assets	(21,199)	(28,785)	(4,239)
Accounts payable	54,127	(23,505)	(9,193)
Accrued payroll and benefit costs	75,556	(39,081)	18,777
Other current and noncurrent liabilities	78,249	(825)	(5,656)
Net cash provided by operating activities	543,931	224,367	296,721
Investing Activities:
Capital expenditures	(56,671)	(44,067)	(36,210)
Acquisition payments, net of cash acquired	(3,707,575)	(27,597)	0
Proceeds from sale of assets	6,721	16,795	12,461
Other investing activities, net	22,376	(5,931)	(10,393)
Net cash used in investing activities	(3,735,149)	(60,800)	(34,142)
Financing Activities:
Proceeds from (Repayments of) Short-term Debt	(11,258)	(29,780)	(1,454)
Proceeds from issuance of long-term debt	5,114,210	1,305,421	1,193,067
Repayments of long-term debt	(1,513,048)	(1,217,434)	(1,318,470)
Repurchase of common stock	(2,901)	(153,049)	(127,169)
Debt issuance costs	(80,231)	(2,707)	0
Payments of Dividends	(30,139)	0	0
Other financing activities, net	(4,108)	12,217	21,068
Net cash provided (used) by financing activities	3,480,741	(109,766)	(275,094)
Effect of exchange rate on cash and cash equivalents	8,710	758	(9,095)
Net change in cash and cash equivalents	298,233	54,559	(21,610)
Cash and cash equivalents at the beginning of period	150,902	96,343	117,953
Cash and cash equivalents at the end of period	449,135	150,902	96,343
Supplemental disclosures:
Cash paid for interest	169,620	65,275	64,702
Cash paid for taxes	$ 56,186	$ 64,531	$ 61,983

ORGANIZATION

ORGANIZATION	12 Months Ended
	Dec. 31, 2020
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 leading provider of business-to-business distribution, logistics services and supply chain solutions. On June 22, 2020, WESCO completed its previously announced acquisition of Anixter International Inc., a Delaware corporation (“Anixter”). Pursuant to the terms of the Agreement and Plan of Merger, dated January 10, 2020 (the “Merger Agreement”), by and among Anixter, WESCO and Warrior Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of WESCO (“Merger Sub”), Merger Sub was merged with and into Anixter (the “Merger”), with Anixter surviving the Merger and continuing as a wholly owned subsidiary of WESCO. On June 23, 2020, Anixter merged with and into Anixter Inc., with Anixter Inc. surviving to become a wholly owned subsidiary of WESCO.

ACCOUNTING POLICIES

ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	2. ACCOUNTING POLICIES Basis of Presentation 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. At the beginning of the third quarter of 2020, in connection with the acquisition of Anixter, the Company identified new operating segments. These operating segments, which have been organized around three strategic business units, consist of Electrical & Electronic Solutions ("EES"), Communications & Security Solutions ("CSS") and Utility & Broadband Solutions ("UBS"). The Company's operating segments, which are equivalent to its reportable segments, are described further in Note 17, "Business Segments". The applicable comparative financial information reported in the Company's previously issued consolidated financial statements for the years ended December 31, 2019 and 2018 has been recast in this Annual Report on Form 10-K to conform to the basis of the new segments. Out-of-Period Adjustment In the fourth quarter of 2020, management determined that the Company’s inventories were overstated by $60.3 million because of a misstatement in inventory cost absorption accounting, which occurred over multiple periods and also impacted inventories acquired in business combinations during those periods. Accordingly, the Consolidated Balance Sheet at December 31, 2020 reflects a reduction to inventories of $60.3 million, an increase to goodwill of $33.9 million and a decrease to deferred income tax liabilities of $12.0 million. The resulting effect of the out-of-period adjustment on the Consolidated Statement of Income and Comprehensive Income for the year ended December 31, 2020 was a $18.9 million increase to cost of goods sold, which decreased net income for the year by $14.4 million. Management concluded that this misstatement is not material to the current period or the financial statements of any previously filed annual or interim periods. Reclassifications The Consolidated Balance Sheet as of December 31, 2019, the Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2019 and 2018, and the Consolidated Statements of Cash Flows for the years ended December 31, 2019 and 2018, respectively, 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 measured as the amount of consideration WESCO expects to receive in exchange for transferring goods or providing 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. However, transfer may occur at a later date depending on the agreed upon terms, such as delivery at the customer's designated location, or based on consignment terms. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. When providing services, sales are recognized over time as control transfers to the customer, which occurs as services are rendered. 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 typically 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 $136.7 million at December 31, 2020 and $81.6 million at December 31, 2019. The supplier volume rebate income as a percentage of net sales was 1.1% in 2020, 1.2% in 2019 and 1.3% in 2018. Cash Equivalents Cash equivalents are defined as highly liquid investments with original maturities of 90 days or less when purchased. Allowance for Expected Credit Losses WESCO recognizes expected credit losses resulting from the inability of its customers to make required payments through an allowance account that is measured each reporting date. WESCO estimates credit losses over the life of its trade accounts receivable using a combination of historical loss data, current credit conditions, specific customer circumstances, and reasonable and supportable forecasts of future economic conditions. The allowance for expected credit losses was $23.9 million at December 31, 2020 and $25.4 million at December 31, 2019. The total amount recorded as selling, general and administrative expense related to credit losses was $10.1 million, $7.0 million and $10.9 million for 2020, 2019 and 2018, 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 reduces the carrying value of its inventories at the earlier of identifying an item that is considered to be obsolete or in excess of supply relative to demand, or no movement in the past 15 months. Reserves for excess and obsolete inventories were $28.7 million and $30.7 million at December 31, 2020 and 2019, respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $15.7 million, $10.0 million and $9.7 million for 2020, 2019 and 2018, respectively. 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 two to ten years for furniture, fixtures and equipment. Costs incurred during the application development stage of internally developing software are capitalized and are reported at the lower of unamortized cost or net realizable value. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Capitalized costs include external direct costs of materials and services consumed in developing internal-use computer software, payroll and payroll-related costs for employees who are directly associated with and who devote time to the internal-use computer software project and interest costs. Internal-use computer software is amortized using the straight-line method over its estimated useful life, typically three to seven years. 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 $399.2 million net book value of property, buildings and equipment as of December 31, 2020, $144.1 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 800 branches, warehouses and sales offices, 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 developed by management, which are categorized as Level 3 of the fair value hierarchy, related to 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. Leases 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. Operating lease expense is recognized on a straight-line basis over the lease term. Operating lease assets and liabilities are recognized at the commencement date based on the present value of the future minimum lease payments. Certain leases contain rent escalation clauses that are either fixed or adjusted periodically for inflation or market rates and such clauses are factored into the Company's determination of lease payments. WESCO also has variable lease payments that do not depend on a rate or index, primarily for items such as common area maintenance and real estate taxes, which are recorded as variable expense when incurred. The operating lease asset includes advance payments and excludes incentives and initial direct costs incurred. 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, or terminate early. 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. For most of WESCO’s leases, the discount rate implicit in the lease is not readily determinable. Accordingly, the Company uses its incremental borrowing rate based on the information available at the lease commencement date to discount lease payments to the present value. 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. The Company first assesses qualitative factors, including macroeconomic conditions, industry and market considerations, cost factors, overall financial performance, other relevant events such as changes in key personnel, changes in the composition or carrying amount of the net assets of a reporting unit, and sustained decreases in share price, to determine whether it is more likely than not that the fair value of WESCO's reporting units are less than their carrying values. If the qualitative assessment indicates that the fair values of the Company's reporting units may not exceed their respective carrying values, then WESCO performs a quantitative test for impairment by comparing the fair value of each reporting unit to its carrying value. The Company determines the fair values of its reporting units using a discounted cash flow analysis and consideration of market multiples. The discounted cash flow analysis uses certain assumptions, including expected operating margins supported by a combination of historical results, current forecasts, market data and recent economic events, which are categorized within Level 3 of the fair value hierarchy. The Company uses a discount rate that reflects market participants' cost of capital. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2020 and 2019, goodwill and indefinite-lived trademarks totaled $4.0 billion and $1.9 billion, respectively. The determination of fair value involves significant management judgment, particularly as it relates to the underlying assumptions and factors around expected operating margins and discount rate. 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. 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. WESCO continually evaluates whether events or circumstances have occurred that would indicate the remaining estimated useful lives of definite lived intangible assets require revision or that the remaining carrying value of such assets may not be recoverable. 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 $27.9 million and $12.9 million at December 31, 2020 and 2019, 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 taxable 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 recognized in the consolidated financial statements. 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 a portion of foreign earnings previously taxed in the U.S. that can effectively be distributed without further material U.S. or foreign taxation, the Company continues to assert that the undistributed earnings of its foreign subsidiaries are indefinitely reinvested. To the extent the earnings of the Company's foreign subsidiaries are distributed in the form of dividends, such earnings may be subject to additional taxes. The Company believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without incurring any material tax cost to repatriate cash held by its foreign subsidiaries. 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. Foreign Currency The local currency is the functional currency for most of the Company's operations outside the U.S. 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). Unrealized gains and losses related to the Company's defined benefit pension obligations are recognized as a component of other comprehensive income (loss) within stockholders' equity. Fair Value of Financial Instruments The Company measures the fair value of assets and liabilities on a recurring and nonrecurring basis 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). The Company measures the fair values of goodwill, intangible assets and property, buildings and equipment on a nonrecurring basis if required by impairment tests applicable to these assets, as described above. Other, net Other non-operating income and expenses ("other, net") primarily includes the non-service cost components of net periodic pension cost (benefit) and foreign exchange gains and losses. 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, "Leases". 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 introduced new guidance for the accounting for credit losses on certain financial instruments. The Company adopted this ASU effective January 1, 2020. The adoption of this new credit loss guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein, and WESCO does not expect it to have a material impact on its financial position or results of operation on an ongoing basis. 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 Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract , which aligned the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The standard was effective for fiscal years beginning after December 15, 2019. The Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. 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. The Company adopted this ASU in the fourth quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. Recently Issued Accounting Pronouncements 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. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting , which provides optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in this Update are effective for all entities as of March 12, 2020 through December 31, 2022. Management is currently evaluating the impact related to the replacement of London Interbank Offered Rate (LIBOR) and whether the Company will elect the adoption of the optional guidance. 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

REVENUE	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer	3. REVENUE WESCO distributes products and provides services to customers globally in various end markets within its business segments. The segments, which consist of Electrical & Electronic Solutions, Communications & Security Solutions, and Utility & Broadband Solutions operate in the United States, Canada and various other international countries. The following tables disaggregate WESCO’s net sales by segment and geography for the periods presented: Year Ended December 31, (In thousands) 2020 2019 2018 Electrical & Electronic Solutions $ 5,479,760 $ 4,860,541 $ 4,878,836 Communications & Security Solutions 3,323,264 909,496 857,481 Utility & Broadband Solutions 3,522,971 2,588,880 2,440,284 Total by segment $ 12,325,995 $ 8,358,917 $ 8,176,601 Year Ended December 31, (In thousands) 2020 2019 2018 United States $ 9,110,453 $ 6,234,119 $ 6,089,130 Canada 1,892,321 1,647,066 1,647,933 Other International (1) 1,323,221 477,732 439,538 Total by geography (2) $ 12,325,995 $ 8,358,917 $ 8,176,601 (1) No individual other international country's net sales are material. (2) WESCO attributes revenues from external customers to individual countries on the basis of point of sale. 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, 2020 and 2019, $24.3 million and $12.3 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, 2020, 2019 and 2018 by approximately $269.5 million, $106.6 million and $107.4 million, respectively. As of December 31, 2020 and 2019, the Company's estimated product return obligation was $38.9 million and $4.4 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 $149.3 million, $71.7 million and $74.1 million for the years ended December 31, 2020, 2019 and 2018, respectively.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	4. FAIR VALUE OF FINANCIAL INSTRUMENTS The Company’s financial instruments primarily consist of cash and cash equivalents, accounts receivable, accounts payable, bank overdrafts, outstanding indebtedness, foreign currency forward contracts, and benefit plan assets. The fair value of the Company's benefit plan assets is disclosed in Note 14, "Employee Benefit Plans" and except for outstanding indebtedness and foreign currency forward contracts, the carrying value of the Company’s remaining financial instruments approximates fair value. 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 carrying value of WESCO's debt instruments with fixed interest rates was $3,730.1 million and $850.0 million as of December 31, 2020 and 2019, respectively. The estimated fair value of this debt was $4,084.7 million and $866.2 million as of December 31, 2020 and 2019, respectively. The reported carrying values of WESCO's indebtedness with variable interest rates approximated their fair values as of December 31, 2020 and 2019. The increase in carrying value and estimated fair value of fixed rate debt is primarily due to higher outstanding borrowings related to the Anixter merger. The Company purchases foreign currency forward contracts to minimize the effect of fluctuating foreign currency-denominated accounts on its earnings. The foreign currency forward contracts are not designated as hedges for accounting purposes. The Company's strategy is to negotiate terms for its derivatives and other financial instruments to be highly effective, such that the change in the value of the derivative offsets the impact of the underlying hedge. Its counterparties to foreign currency forward contracts have investment-grade credit ratings. The Company regularly monitors the creditworthiness of its counterparties to ensure no issues exist that could affect the value of its derivatives. The Company does not hedge 100% of its foreign currency-denominated accounts. In addition, the results of hedging can vary significantly based on various factors, such as the timing of executing foreign currency forward contracts versus the movement of currencies as well as the fluctuations in the account balances throughout each reporting period. The fair value of foreign currency forward contracts is based on the difference between the contract rate and the current exchange rate. The fair value of foreign currency forward contracts is measured using observable market information. These inputs would be considered Level 2 in the fair value hierarchy. At December 31, 2020, foreign currency forward contracts were revalued at then-current foreign exchange rates with the changes in valuation reflected directly in other non-operating expenses ("other, net") in the Consolidated Statements of Income and Comprehensive Income offsetting the transaction gain (loss) recorded on foreign currency-denominated accounts. At December 31, 2020, the gross and net notional amounts of foreign currency forward contracts outstanding were approximately $111.9 million. While all of the Company's foreign currency forward contracts are subject to master netting arrangements with its counterparties, assets and liabilities related to these contracts are presented on a gross basis within the Consolidated Balance Sheets. The gross fair values of assets and liabilities related to foreign currency forward contracts were immaterial.
Derivatives and Fair Value	The Company purchases foreign currency forward contracts to minimize the effect of fluctuating foreign currency-denominated accounts on its earnings. The foreign currency forward contracts are not designated as hedges for accounting purposes. The Company's strategy is to negotiate terms for its derivatives and other financial instruments to be highly effective, such that the change in the value of the derivative offsets the impact of the underlying hedge. Its counterparties to foreign currency forward contracts have investment-grade credit ratings. The Company regularly monitors the creditworthiness of its counterparties to ensure no issues exist that could affect the value of its derivatives. The Company does not hedge 100% of its foreign currency-denominated accounts. In addition, the results of hedging can vary significantly based on various factors, such as the timing of executing foreign currency forward contracts versus the movement of currencies as well as the fluctuations in the account balances throughout each reporting period. The fair value of foreign currency forward contracts is based on the difference between the contract rate and the current exchange rate. The fair value of foreign currency forward contracts is measured using observable market information. These inputs would be considered Level 2 in the fair value hierarchy. At December 31, 2020, foreign currency forward contracts were revalued at then-current foreign exchange rates with the changes in valuation reflected directly in other non-operating expenses ("other, net") in the Consolidated Statements of Income and Comprehensive Income offsetting the transaction gain (loss) recorded on foreign currency-denominated accounts. At December 31, 2020, the gross and net notional amounts of foreign currency forward contracts outstanding were approximately $111.9 million. While all of the Company's foreign currency forward contracts are subject to master netting arrangements with its counterparties, assets and liabilities related to these contracts are presented on a gross basis within the Consolidated Balance Sheets. The gross fair values of assets and liabilities related to foreign currency forward contracts were immaterial.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	5. GOODWILL AND INTANGIBLE ASSETS Goodwill The following table sets forth the changes in the carrying value of goodwill: Year Ended December 31, 2020 EES CSS UBS Total (In thousands) Beginning balance January 1, 2020 $ 573,447 $ 235,711 $ 949,882 $ 1,759,040 Adjustments to goodwill for acquisitions (Note 6) (1) (2) (3) (4) 264,538 868,936 250,553 1,384,027 Foreign currency exchange rate changes 15,471 10,853 17,778 44,102 Ending balance December 31, 2020 (4) $ 853,456 $ 1,115,500 $ 1,218,213 $ 3,187,169 (1) Adjustments to goodwill include the final allocation of the purchase price paid for SLS, which is reflected in the EES segment. (2) Adjustments to goodwill include an increase of $33.9 million resulting from the out-of-period adjustment related to inventory cost absorption accounting, as described in Note 2, "Accounting Policies", which affected the EES, CSS and UBS segments by $20.2 million, $2.0 million, and $11.7 million, respectively. (3) The effect of the merger with Anixter on the Company's reportable segments is disclosed in Note 17, "Business Segments". (4) Adjustments to goodwill include $26.1 million that is classified as held for sale on the UBS segment , as disclosed in Note 7, "Assets and Liabilities Held for Sale". Year Ended December 31, 2019 EES CSS UBS Total (In thousands) Beginning balance January 1, 2019 $ 542,704 $ 234,449 $ 945,450 $ 1,722,603 Adjustments to goodwill for acquisitions (Note 6) 5,767 — — 5,767 Foreign currency exchange rate changes 24,976 1,262 4,432 30,670 Ending balance December 31, 2019 $ 573,447 $ 235,711 $ 949,882 $ 1,759,040 Certain triggering events occurred during the first quarter of 2020, including the effect of the ongoing macroeconomic disruption and uncertainty caused by the COVID-19 pandemic, as well as the decline in the Company's share price and market capitalization, both of which indicated that the carrying value of goodwill and indefinite-lived intangible assets may not be recoverable. Accordingly, the Company performed an interim test for impairment as of March 31, 2020. There were no impairment losses identified as a result of this interim test. As disclosed in Note 2, "Accounting Policies", the Company identified new operating segments during the third quarter of 2020, which changed the composition of its reporting units. Accordingly, the Company reassigned goodwill to the new reporting units using a relative fair value allocation approach. The Company performed a goodwill impairment test immediately before and after it reorganized its reporting structure. Goodwill was tested for impairment on a reporting unit level and the evaluation involved comparing the fair value of each reporting unit to its carrying value. The fair values of the Company's reporting units were determined using a discounted cash flow analysis, and consideration was also given to market multiples. In performing the quantitative assessments, management used expected operating margins supported by a combination of historical results, current forecasts, market data and recent economic events, which are categorized within Level 3 of the fair value hierarchy. The Company used a discount rate that reflects market participants' cost of capital. There were no impairment losses identified as a result of these tests. Although all of the Company's reorganized reporting units had fair values that exceeded the respective carrying values, the EES reporting unit with goodwill of $809.9 million had an estimated fair value that exceeded its respective carrying value by less than 10%. As a result, the EES reporting unit is more susceptible to impairment risk from adverse macroeconomic conditions and if such conditions were to persist the underlying cash flows used to estimate fair value may impact the recoverability of goodwill. The Company performed its annual impairment tests of goodwill and indefinite-lived intangible assets during the fourth quarter by assessing qualitative factors to determine whether it was more likely than not that the fair value of a reporting unit was less than its carrying amount. In performing this qualitative assessment, the Company assessed relevant events and circumstances, including macroeconomic conditions, industry and market considerations, cost factors, overall financial performance, other relevant events such as changes in key personnel, changes in the composition or carrying amount of the net assets of a reporting unit, and sustained decreases in share price. As a result of this assessment, the Company determined that the fair values of its reporting units continued to exceed the respective carrying amounts and, therefore, a quantitative impairment test was unnecessary. The determination of fair value of the reporting units involves significant management judgment, particularly as it relates to the underlying assumptions and factors around expected operating margins and discount rate. Due to the ongoing uncertainty surrounding the current macroeconomic environment and conditions in the markets in which WESCO operates, as well as the risk that the Company may not fully realize cost savings, operating synergies or revenue improvement as a result of its acquisition of Anixter, there can be no assurance that the fair values of the Company's reporting units will exceed their carrying values in the future, and that goodwill and indefinite-lived intangible assets will be fully recoverable. Intangible Assets The components of intangible assets are as follows: December 31, 2020 December 31, 2019 Life (in years) Gross Carrying Amount (1) Accumulated Amortization (1) Net Gross Carrying Amount (1) Accumulated Amortization (1) Net (In thousands) Intangible assets: Trademarks Indefinite $ 833,793 $ — $ 833,793 $ 98,699 $ — $ 98,699 Customer relationships (2) 10 - 20 1,434,554 (227,585) 1,206,969 358,341 (201,962) 156,379 Distribution agreements (2) 10 - 19 29,212 (21,040) 8,172 37,371 (25,294) 12,077 Trademarks (2) 10 - 15 24,898 (11,415) 13,483 24,800 (9,319) 15,481 Non-compete agreements 2 - 5 4,462 (1,384) 3,078 196 (180) 16 Patents 10 — — — 48,310 (43,687) 4,623 $ 2,326,919 $ (261,424) $ 2,065,495 $ 567,717 $ (280,442) $ 287,275 (1) Excludes the original cost and related accumulated amortization of fully-amortized intangible assets. (2) The net carrying amount as of December 31, 2020 excludes $1.0 million of trademarks, $3.3 million of customer relationships and $1.4 million of distribution agreements that are classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale". Amortization expense related to intangible assets totaled $66.5 million, $35.5 million and $35.9 million for the years ended December 31, 2020, 2019 and 2018, 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) 2021 $ 86,619 2022 83,628 2023 81,400 2024 80,087 2025 76,829 Thereafter 823,139

ACQUISITIONS

ACQUISITIONS	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
ACQUISITIONS	6. ACQUISITIONS Anixter International Inc. As described in Note 1, "Organization", on June 22, 2020, WESCO completed its previously announced merger with Anixter. The Company used the net proceeds from the issuance of senior unsecured notes, borrowings under its revolving credit facility and accounts receivable securitization facility (as described further in Note 10, "Debt"), as well as cash on hand, to finance the acquisition of Anixter and related transaction costs. At the effective time of the Merger, each outstanding share of common stock of Anixter (subject to limited exceptions) was converted into the right to receive (i) $72.82 in cash, (ii) 0.2397 shares of common stock of WESCO, par value $0.01 per share (the “WESCO Common Stock”) and (iii) 0.6356 depositary shares, each representing a 1/1,000th interest in a share of newly issued fixed-rate reset cumulative perpetual preferred stock of WESCO, Series A, with a $25,000 stated amount per whole preferred share and an initial dividend rate equal to 10.625%. Anixter is a leading distributor of network and security solutions, electrical and electronic solutions, and utility power solutions with locations in over 300 cities across approximately 50 countries, and 2019 annual sales of more than $8 billion. The Merger brought together two companies with highly compatible capabilities and characteristics. The combination of WESCO and Anixter created an enterprise with scale and should afford the Company the opportunity to digitize its business, and expand its services portfolio and supply chain offerings. The total preliminary estimated fair value of consideration transferred for the Merger consisted of the following: (In thousands) Cash portion attributable to common stock outstanding $ 2,476,010 Cash portion attributable to options and restricted stock units outstanding 87,375 Fair value of cash consideration 2,563,385 Common stock consideration 313,512 Series A preferred stock consideration 573,786 Fair value of equity consideration 887,298 Extinguishment of Anixter obligations, including accrued and unpaid interest 1,247,653 Total purchase consideration $ 4,698,336 Supplemental cash flow disclosure related to acquisitions: Cash paid for acquisition $ 3,811,038 Less: Cash acquired (103,463) Cash paid for acquisition, net of cash acquired $ 3,707,575 The Merger was accounted for as a business combination with WESCO acquiring Anixter in accordance with Accounting Standards Codification (“ASC”) 805, Business Combinations . Under the acquisition method of accounting, the preliminary purchase consideration was allocated to the identified assets acquired and liabilities assumed based on their respective acquisition date fair value, with any excess allocated to goodwill. The fair value estimates were based on income, market and cost valuation methods using primarily unobservable inputs developed by management, which are categorized within Level 3 of the fair value hierarchy. Specifically, the fair values of the identified trademark and customer relationship intangible assets were estimated using the relief-from-royalty and multi-period excess earnings methods, respectively. Significant inputs used to value these identifiable intangible assets included projected revenues and expected operating margins, customer attrition rates, discount rates, royalty rates, and applicable income tax rates. The excess purchase consideration recorded to goodwill is not deductible for income tax purposes, and has been assigned to the Company's reportable segments based on their relative fair values, as disclosed in Note 5, "Goodwill and Intangible Assets". The resulting goodwill is primarily attributable to Anixter's workforce, significant cross-selling opportunities in additional geographies, enhanced scale, and other operational efficiencies. Since the initial measurement of the identified assets acquired and liabilities assumed, the Company has recognized adjustments to inventories of $8.2 million, operating lease assets of $18.0 million, total identifiable intangible assets of $5.4 million, other noncurrent assets of $15.5 million, operating lease liabilities of $17.0 million, deferred income taxes of $27.5 million and other noncurrent liabilities of $38.7 million. Certain other measurement period adjustments were made to the identified assets acquired and liabilities assumed, none of which were significant, individually or in aggregate. The net impact of these adjustments was an increase to goodwill of $2.4 million. The estimated fair values of assets acquired and liabilities assumed are based on preliminary calculations and valuations using estimates and assumptions at the time of acquisition. The determination of the fair values of assets acquired and liabilities assumed, especially those related to identifiable intangible assets, is preliminary due to the complexity of combining multibillion dollar businesses. Accordingly, as the Company obtains additional information during the measurement period (not to exceed one year from the acquisition date), estimates and assumptions for the preliminary purchase consideration allocations may change materially. The following table sets forth the preliminary allocation of the purchase consideration to the respective fair value of assets acquired and liabilities assumed for the acquisition of Anixter: (In thousands) Assets Cash and cash equivalents $ 103,463 Trade accounts receivable 1,306,900 Other accounts receivable 116,386 Inventories 1,416,582 Prepaid expenses and other current assets 54,978 Property, buildings and equipment 211,721 Operating lease assets 280,285 Intangible assets 1,838,065 Goodwill 1,370,396 Other assets 139,760 Total assets $ 6,838,536 Liabilities Accounts payable $ 920,163 Accrued payroll and benefit costs 69,480 Short-term debt and current portion of long-term debt 13,225 Other current liabilities 222,119 Long-term debt 77,617 Operating lease liabilities 217,303 Deferred income taxes 374,734 Other noncurrent liabilities 245,559 Total liabilities $ 2,140,200 Fair value of net assets acquired, including goodwill and intangible assets $ 4,698,336 The following table sets forth the preliminary identifiable intangible assets and their estimated weighted-average useful lives: Identifiable Intangible Assets Estimated Weighted-Average Estimated Useful Life in Years (1) (In thousands) Customer relationships $ 1,098,900 19 Trademarks 735,000 Indefinite Non-compete agreements 4,165 2 Total identifiable intangible assets $ 1,838,065 (1) Measurement period adjustments include an update to the estimated useful lives initially assigned to customer relationships, which resulted in income of $6.4 million during the year ended December 31, 2020. The results of operations of Anixter are included in the consolidated financial statements beginning on June 22, 2020, the acquisition date. For the year ended December 31, 2020, the consolidated statement of income includes $4.5 billion of net sales and $180.0 million of income from operations for Anixter. Transaction costs related to the merger were comprised of legal, advisory and other costs of $132.2 million, which are included in selling, general and administrative expenses for the year ended December 31, 2020. Pro Forma Financial Information The following unaudited pro forma financial information presents combined results of operations for the periods presented, as if the Company had completed the Merger on January 1, 2019. The unaudited pro forma financial information includes adjustments to amortization and depreciation for intangible assets and property, buildings and equipment, adjustments to interest expense for the additional indebtedness incurred to complete the acquisition (including the amortization of debt discount and issuance costs), transaction costs, change in control and severance costs, dividends accrued on the Series A preferred stock, compensation expense associated with the WESCO phantom stock unit awards described in Note 14, "Employee Benefit Plans", as well as the respective income tax effects of such adjustments. For the year ended December 31, 2020, adjustments totaling $7.0 million increased the unaudited pro forma net income attributable to common stockholders, and adjustments totaling $201.3 million decreased the unaudited pro forma net income attributable to common stockholders for the year ended December 31, 2019. The unaudited pro forma financial information does not reflect any cost savings, operating synergies or revenue enhancements that WESCO may achieve as a result of its acquisition of Anixter, the costs to integrate the operations of WESCO and Anixter or the costs necessary to achieve these cost savings, operating synergies and revenue enhancements. The unaudited pro forma financial information presented below is not necessarily indicative of consolidated results of operations of the combined business had the acquisition occurred at the beginning of the respective fiscal years, nor is it necessarily indicative of future results of operations of the combined company. Year Ended (In thousands) December 31, 2020 December 31, 2019 Pro forma net sales $ 16,016,902 $ 17,204,472 Pro forma net income attributable to common stockholders 119,839 285,100 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 then outstanding 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 $11.6 million, which is deductible for tax purposes. The following table sets forth the consideration paid for the acquisition of SLS: Year Ended December 31, 2019 (In thousands) Fair value of assets acquired $ 34,812 Fair value of liabilities assumed 7,070 Cash paid for acquisition $ 27,742

ASSETS AND LIABILITIES HELD FOR

ASSETS AND LIABILITIES HELD FOR SALE	12 Months Ended
	Dec. 31, 2020
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations, Disclosure	7. ASSETS AND LIABILITIES HELD FOR SALE On August 6, 2020, the Company entered into a Consent Agreement with the Competition Bureau of Canada regarding the merger with Anixter. Under the Consent Agreement, the Company agreed to divest certain legacy WESCO businesses in Canada, which had total sales of approximately $120 million in 2019. Accordingly, the Company determined that the assets and liabilities of these legacy WESCO businesses in Canada met the held for sale criteria as of December 31, 2020. These businesses did not meet the criteria to be classified as discontinued operations. The assets and liabilities classified as held for sale were as follows: As of December 31, 2020 (In thousands) Trade accounts receivable, net $ 4,258 Inventories 16,438 Prepaid expenses and other current assets 395 Property, buildings and equipment, net 263 Operating lease assets 1,938 Intangible assets, net 5,722 Goodwill 26,059 Total assets held for sale $ 55,073 Accounts payable $ 3,639 Other current liabilities 541 Operating lease liabilities 1,537 Total liabilities held for sale $ 5,717

PROPERTY, BUILDINGS AND EQUIPME

PROPERTY, BUILDINGS AND EQUIPMENT	12 Months Ended
	Dec. 31, 2020
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, 2020 (1) 2019 (In thousands) Buildings and leasehold improvements $ 169,873 $ 110,056 Furniture, fixtures and equipment 266,317 162,029 Software costs 235,666 127,919 671,856 400,004 Accumulated depreciation and amortization (312,106) (268,415) 359,750 131,589 Land 26,409 24,106 Construction in progress 12,998 25,753 $ 399,157 $ 181,448 (1) The components of property, buildings and equipment as of December 31, 2020 exclude a total of $0.3 million that is classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale". Depreciation expense was $40.8 million, $15.9 million and $17.3 million, and capitalized software amortization was $14.3 million, $10.6 million and $9.8 million, in 2020, 2019 and 2018, respectively. The unamortized software cost was $123.9 million and $29.8 million as of December 31, 2020 and 2019, respectively. Furniture, fixtures and equipment include finance leases of $25.7 million and $6.5 million and related accumulated amortization of $7.9 million and $5.1 million as of December 31, 2020 and 2019, respectively.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Lessee, Operating Leases	9. LEASES WESCO leases substantially all of its real estate, as well as automobiles, trucks and other equipment under lease arrangements classified as operating. The Company's finance leases, which are recorded in the Consolidated Balance Sheets 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 periods presented: As of December 31, (In thousands) 2020 (1) 2019 Operating lease assets $ 534,705 $ 235,834 Current operating lease liabilities (2) 128,322 62,046 Noncurrent operating lease liabilities 414,889 179,830 Total operating lease liabilities $ 543,211 $ 241,876 (1) Operating lease assets and liabilities of $1.9 million and $2.1 million, respectively, are classified as held for sale as of December 31, 2020, as disclosed in Note 7, "Assets and Liabilities Held for Sale". (2) Current operating lease liabilities are recorded as a component of other current liabilities in the Consolidated Balance Sheets. 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 periods presented: Year Ended December 31, (In thousands) 2020 2019 Operating lease cost $ 127,725 $ 73,613 Short-term lease cost 494 90 Variable lease cost 36,230 23,385 Total lease cost $ 164,449 $ 97,088 Variable lease cost consists of the non-lease components described in Note 2, "Accounting Policies", 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 periods presented: Year Ended December 31, (In thousands) 2020 2019 Operating cash flows from operating leases $ 117,106 $ 75,775 Right-of-use assets obtained in exchange for new operating lease liabilities 121,207 60,586 As of December 31, 2020 and 2019, the weighted-average remaining lease term for operating leases was 6.1 years and 5.3 years, respectively. The weighted-average discount rate used to measure operating leases was 4.6% as of December 31, 2020 and 2019. 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 Consolidated Balance Sheet as of December 31, 2020: (In thousands) 2021 $ 155,071 2022 127,851 2023 100,746 2024 72,847 2025 46,730 Thereafter 124,127 Total undiscounted operating lease payments 627,372 Less: imputed interest (84,161) Total operating lease liabilities $ 543,211 Operating lease payments include $17.4 million related to options to extend lease terms that are reasonably certain of being exercised. As of December 31, 2020, the Company has additional leases related to facilities that have not yet commenced of $2.6 million. These operating leases will commence in 2021 with lease terms of seven to ten years.

DEBT

DEBT	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
DEBT	10. DEBT The following table sets forth WESCO’s outstanding indebtedness: As of December 31, 2020 2019 (In thousands) International lines of credit $ 29,575 $ 26,255 Accounts Receivable Securitization Facility 950,000 415,000 Revolving Credit Facility 250,000 — 5.375% Senior Notes due 2021 500,000 500,000 5.50% Senior Notes due 2023 58,636 — 5.375% Senior Notes due 2024 350,000 350,000 6.00% Senior Notes due 2025 4,173 — 7.125% Senior Notes due 2025 1,500,000 — 7.250% Senior Notes due 2028, less debt discount of $9,332 1,315,668 — Finance lease obligations 17,931 1,373 Total debt 4,975,983 1,292,628 Plus: Fair value adjustment to the Anixter Senior Notes 1,650 — Less: Unamortized debt issuance costs (78,850) (8,876) Less: Short-term debt and current portion of long-term debt (528,830) (26,685) Total long-term debt $ 4,369,953 $ 1,257,067 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 $31.0 million. The international lines of credit generally are renewable on an annual basis and certain facilities are fully and unconditionally guaranteed by WESCO Distribution. Accordingly, certain borrowings under these lines directly reduce availability under the Revolving Credit Facility. The applicable interest rate for borrowings under these lines of credit varies by country and is governed by the applicable loan agreement. The average interest rate for these facilities was 3.40% and 6.32% at December 31, 2020 and 2019, respectively. Accounts Receivable Securitization Facility On June 22, 2020, WESCO Distribution amended its accounts receivable securitization facility (the “Receivables Facility”) pursuant to the terms and conditions of a Fifth Amended and Restated Receivables Purchase Agreement (the “Receivables Purchase Agreement”), 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 Purchase Agreement amends and restates the amended and restated receivables purchase agreement entered into on September 24, 2015 (the “Existing Receivables Purchase Agreement”). The Receivables Purchase Agreement, among other things, increased the purchase limit under the Existing Receivables Purchase Agreement from $600 million to $1,025 million, with the opportunity to exercise an accordion feature that permits increases in the purchase limit of up to $375 million, extended the term of the Receivables Facility to June 22, 2023 and added and amended certain defined terms. Borrowings under the Receivables Facility bear interest at the 30-day LIBOR rate, with a LIBOR floor of 0.5%, plus applicable spreads. The interest rate spread of the Receivables Facility increased from 0.95% to 1.20%. The commitment fee remained unchanged at 0.45%. On December 14, 2020, WESCO Distribution amended its Receivables Facility pursuant to the terms and conditions of a First Amendment to the Fifth Amended and Restated Receivables Purchase Agreement (the “Receivables Amendment”). The Receivables Amendment amends the Receivables Purchase Agreement and permits an increase to the purchase limit from $1,025 million to $1,200 million. The maturity date, interest rate spread, and commitment fee of the Receivables Facility remain unchanged. 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, 2020 and 2019, accounts receivable eligible for securitization totaled $1,476.1 million and $809.5 million, respectively. The Consolidated Balance Sheets as of December 31, 2020 and 2019 include $950.0 million and $415.0 million, respectively, of accounts receivable balances legally sold to third parties, as well as borrowings for equal amounts. At December 31, 2020, the interest rate for this facility was approximately 1.6%. Revolving Credit Facility On June 22, 2020, WESCO, WESCO Distribution and certain other subsidiaries of WESCO entered into a $1,100 million revolving credit facility (the “Revolving Credit Facility”), as a replacement of WESCO Distribution’s revolving credit facility entered into on September 26, 2019, pursuant to the terms and conditions of a Fourth Amended and Restated Credit Agreement, dated as of June 22, 2020 (the “Revolving Credit Agreement”), among WESCO Distribution, the other U.S. borrowers party thereto (collectively, the “U.S. Borrowers”), WESCO Distribution Canada LP (“WESCO Canada”), the other Canadian borrowers party thereto (collectively, the “Canadian Borrowers”), WESCO, the lenders party thereto and Barclays Bank PLC, as the administrative agent. The Revolving Credit Facility contains a letter of credit sub-facility of up to $175 million and an accordion feature allowing WESCO Distribution to request increases to the borrowing commitments under the Revolving Credit Facility of up to $500 million in the aggregate, subject to customary conditions. The Revolving Credit Facility matures in June 2025. On December 14, 2020, WESCO Distribution and certain other subsidiaries of WESCO entered into an amendment to the Revolving Credit Facility pursuant to the terms and conditions of a First Amendment to Fourth Amended and Restated Credit Agreement, dated as of December 14, 2020 (the “Revolver Amendment”), among WESCO Distribution, the other U.S. borrowers party thereto, WESCO Distribution Canada LP, the other Canadian borrowers party thereto, WESCO, the lenders party thereto and Barclays Bank PLC, as administrative agent. The Revolver Amendment permits an increase to the revolving commitments from $1,100 million to $1,200 million and amends certain other defined terms. No other material terms were changed. The obligations of WESCO Distribution and the other U.S. Borrowers under the Revolving Credit Facility have been guaranteed by WESCO and certain of WESCO Distribution’s subsidiaries (including certain subsidiaries of Anixter). The obligations of WESCO Canada and the other Canadian Borrowers under the Revolving Credit Facility (including certain subsidiaries of Anixter) have been guaranteed by certain subsidiaries of WESCO Canada and the other Canadian Borrowers. The Revolving Credit Facility is secured by (i) substantially all assets of WESCO Distribution, the other U.S. Borrowers and certain of WESCO Distribution’s subsidiaries (including certain subsidiaries of Anixter), 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, the other Canadian Borrowers and certain of WESCO Canada’s subsidiaries, other than, among other things, real property, in each case, subject to customary exceptions and limitations. 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, 2020, the interest rate for this facility was approximately 1.6%. The Revolving Credit Agreement requires compliance with conditions that must be satisfied prior to any borrowing as well as ongoing compliance with certain customary affirmative and negative covenants. The Revolving Credit Agreement contains customary events of default. Upon the occurrence and during the continuance of an event of default, the commitments of the lenders may be terminated, and all outstanding obligations of the loan parties under the Revolving Credit Facility may be declared immediately due and payable. During 2020, WESCO borrowed $1,197.9 million under the prior and new revolving credit facilities and made repayments in the aggregate amount of $948.0 million. During 2019, aggregate borrowings and repayments under prior revolving credit agreements were $715.4 million and $767.4 million, respectively. WESCO had $801.5 million available under the Revolving Credit facility at December 31, 2020, after giving effect to $48.5 million of outstanding letters of credit, as compared to $563.8 million available under the prior 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. 5.375% Senior Notes due 2021 In November 2013, WESCO Distribution issued $500 million aggregate principal amount of 5.375% Senior Notes due 2021 (the "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% per annum, 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 are 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 and at any time all or a part may be redeemed by WESCO Distribution. 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. On December 15, 2020, WESCO Distribution exercised its right to redeem the entire $500 million aggregate principal amount of the 2021 Notes, and U.S. Bank, National Association, as trustee under the indenture governing the 2021 Notes, issued a notice of redemption to registered holders of the 2021 Notes. The date fixed for the redemption of the 2021 Notes is January 14, 2021 (the “Redemption Date”). The 2021 Notes will be redeemed at a redemption price equal to 100% of the principal amount of the 2021 Notes plus accrued interest on the 2021 Notes to, but not including, the Redemption Date. 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 stated 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 are recorded as a reduction to the carrying value of the debt and are being amortized over the life of the notes. The 2024 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. Any time 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. 5.50% Senior Notes due 2023 6.00% Senior Notes due 2025 On April 30, 2020, in connection with the Merger, WESCO Distribution commenced offers to purchase for cash (each, a “WESCO Tender Offer” and, together the “WESCO Tender Offers”) any and all of Anixter Inc.’s outstanding (i) 5.50% Senior Notes due 2023 (the “Anixter 2023 Senior Notes”), $350.0 million aggregate principal amount, issued under the Indenture, dated as of August 18, 2015 (the “Anixter 2023 Indenture”), by and among Anixter Inc., Anixter and Wells Fargo Bank, National Association, as trustee, and (ii) 6.00% Senior Notes due 2025 (the “Anixter 2025 Senior Notes” and, together with the Anixter 2023 Senior Notes, the "Anixter Senior Notes"), $250.0 million aggregate principal amount, issued under the Indenture, dated as of November 13, 2018 (the “Anixter 2025 Indenture” and, together with the Anixter 2023 Indenture, the “Anixter Indentures”) by and among Anixter Inc., Anixter and Wells Fargo Bank, National Association, as trustee. Concurrent with the WESCO Tender Offers, Anixter Inc. commenced consent solicitations to amend the definition of "Change of Control" under the applicable Indenture to exclude the Merger and related transactions and expressly permit a merger between Anixter Inc. and Anixter (the “Anixter Consent Solicitations”). On June 23, 2020 (the "Expiration Date"), following the completion of the Merger, the WESCO Tender Offers and Anixter Consent Solicitations expired and settled. Pursuant to the terms of the Offer to Purchase and Consent Solicitation Statement, dated April 30, 2020, holders of the Anixter Senior Notes that validly tendered and did not validly withdraw prior to such date, received total tender offer consideration of $1,012.50 per $1,000 principal amount of Anixter Senior Notes, which amount, in each case, included an early tender payment of $50.00 per $1,000 principal amount of Anixter Senior Notes. Holders who validly delivered their consents at or prior to the Expiration Date received a consent fee of $2.50 per $1,000 principal amount of Anixter Senior Notes. As of December 31, 2020, $58.6 million and $4.2 million aggregate principal amount of the Anixter 2023 Senior Notes and Anixter 2025 Senior Notes, respectively, were outstanding. 7.125% Senior Notes due 2025 7.250% Senior Notes due 2028 On June 12, 2020, WESCO Distribution issued $1,500 million aggregate principal amount of 7.125% Senior Notes due 2025 (the “2025 Notes”) and $1,325 million aggregate principal amount of 7.250% Senior Notes due 2028 (the “2028 Notes” and, together with the 2025 Notes, the “Notes”). The 2025 Notes were issued at a price of 100.000% of the aggregate principal amount. The 2028 Notes were issued at a price of 99.244% of the aggregate principal amount. WESCO incurred costs related to the issuance of the 2025 Notes and 2028 Notes totaling $33.1 million and $29.3 million, respectively, which were recorded as a reduction to the carrying value of the debt and are being amortized over the respective lives of the notes. The Notes were issued pursuant to, and are governed by, an indenture (the “Notes Indenture”), dated as of June 12, 2020, between the Company, WESCO Distribution and U.S. Bank National Association, as trustee (the “Trustee”). The Notes and related guarantees were issued in a private transaction exempt from the Securities Act of 1933, as amended (the “Securities Act”) and have not been, and will not be, registered under the Securities Act and may not be offered or sold in the U.S. absent registration or an applicable exemption from, or in a transaction not subject to the registration requirements of the Securities Act and other applicable securities laws. The Company used the net proceeds from the issuance of the Notes, together with borrowings under its new and amended credit facilities and existing cash on hand, to finance the Merger and the other transactions contemplated by the Merger Agreement. The use of proceeds included (i) paying the cash portion of the Merger consideration to stockholders of Anixter, (ii) refinancing certain existing indebtedness of Anixter contemplated by the Merger Agreement, including financing the satisfaction and discharge, defeasance, redemption or other repayment in full of the 5.125% Senior Notes due 2021 of Anixter Inc., a wholly owned subsidiary of Anixter, and financing payments in connection with the Anixter Consent Solicitations and WESCO Tender Offers, as described above, (iii) refinancing other indebtedness of the Company, and (iv) paying fees, costs and expenses in connection with the foregoing. The Notes are unsecured and unsubordinated obligations of WESCO Distribution and are guaranteed on an unsecured, unsubordinated basis by the Company and Anixter Inc. The 2025 Notes accrue interest at a rate of 7.125% per annum, payable semi-annually in arrears on June 15 and December 15 of each year. The 2025 Notes will mature on June 15, 2025. The 2028 Notes accrue interest at a rate of 7.250% per annum, payable semi-annually in arrears on June 15 and December 15 of each year. The 2028 Notes will mature on June 15, 2028. WESCO Distribution may redeem all or a part of the 2025 Notes at any time prior to June 15, 2022 by paying a “make-whole” premium plus accrued and unpaid interest, if any, to but excluding the redemption date. In addition, at any time prior to June 15, 2022, WESCO Distribution may redeem up to 35% of the 2025 Notes with the net cash proceeds from certain equity offerings. On or after June 15, 2022, WESCO Distribution may redeem all or a part of the 2025 Notes on the redemption dates and at the redemption prices specified in the Notes Indenture. WESCO Distribution may redeem all or a part of the 2028 Notes at any time prior to June 15, 2023 by paying a “make-whole” premium plus accrued and unpaid interest, if any, to but excluding the redemption date. In addition, at any time prior to June 15, 2023, WESCO Distribution may redeem up to 35% of the 2028 Notes with the net cash proceeds from certain equity offerings. On or after June 15, 2023, WESCO Distribution may redeem all or a part of the 2028 Notes on the redemption dates and at the redemption prices specified in the Notes Indenture. The Notes Indenture contains certain covenants that, among other things, limit (i) the Company’s and its subsidiaries’ ability to pay dividends on or repurchase the Company’s capital stock, incur liens on assets, engage in certain sale and leaseback transactions or sell certain assets, and (ii) the Company’s and any guarantor’s ability to sell all or substantially all of its assets to, or merge or consolidate with or into, other persons, in the case of each of the foregoing, subject to certain qualifications and exceptions, including the termination of certain of these covenants upon the Notes receiving investment grade credit ratings. The Notes Indenture contains certain events of default, including, among other things, failure to make required payments, failure to comply with certain agreements or covenants, failure to pay or acceleration of certain other indebtedness, certain events of bankruptcy and insolvency, and failure to pay certain judgments. An event of default under the Notes Indenture will allow either the Trustee or the holders of at least 25% in aggregate principal amount of the applicable series of the then-outstanding Notes to accelerate, or in certain cases, will automatically cause the acceleration of the amounts due under the applicable series of Notes. 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, 2020 and 2019, unamortized debt issuance costs of $78.9 million and $8.9 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, 2020. The following table sets forth the aggregate principal repayment requirements for all indebtedness for the next five years and thereafter, as of December 31, 2020: (In thousands) 2021 $ 529,869 2022 4,051 2023 1,016,322 2024 352,183 2025 1,756,055 Thereafter 1,326,835 Total payments on debt $ 4,985,315 Debt discount (9,332) Total debt $ 4,975,983 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.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity Note [Abstract]
CAPITAL STOCK	11. STOCKHOLDERS' EQUITY 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. Series A Preferred Stock The Company's Board of Directors authorized 25,000 shares of fixed-rate reset cumulative perpetual preferred stock, Series A, with a liquidation preference of $25,000 per whole preferred share and a par value of $0.01 per share (the "Series A Preferred Stock"). Depositary shares, each representing a 1/1,000th interest in a share of Series A Preferred Stock, are registered under the Securities Act of 1933, as amended. In connection with the Merger, as described in Note 6, "Acquisitions", the Company issued 21,611,534 depositary shares, representing an interest in approximately 21,612 shares of Series A Preferred Stock. Holders of shares of the Series A Preferred Stock are entitled to receive, when, as and if declared by the Company's Board of Directors, cumulative cash dividends at an initial rate of 10.625% per annum of the $25,000 liquidation preference per share. On June 22, 2025, and every five-year period thereafter, the dividend rate on the Series A Preferred Stock resets and will be equal to the Five-year U.S. Treasury Rate plus a spread of 10.325%. Holders of the Series A Preferred Stock are not entitled to convert or exchange their shares of Series A Preferred stock into shares of any of WESCO’s other classes or series of stock or into any other security of WESCO (other than upon a change of control involving the issuance of additional shares of common stock or other change of control transaction, in each case, approved by holders of common stock). The Series A Preferred Stock has no stated maturity and will not be subject to any sinking fund, retirement fund or purchase fund or any other obligation of WESCO to redeem, repurchase or retire the Series A Preferred Stock. Holders of the Series A Preferred Stock will have limited voting rights, including the right to elect two directors to the board of directors of the Company in the event dividends on the Series A Preferred Stock remain unpaid for the equivalent of six or more full quarterly dividend periods. 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, 2024 Notes, 2025 Notes and 2028 Notes, place certain limits on the Company's ability to declare or pay dividends and repurchase common stock. The share repurchases in 2019 and 2018, as described in Note 13, "Earnings Per Share", were made within the limits of WESCO's various credit agreements. At December 31, 2020 and 2019, 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. Stockholder Rights Plan On July 17, 2020, WESCO's Board of Directors declared a dividend of one preferred share purchase right (a “Right”) for each outstanding share of common stock of WESCO, par value $0.01 per share (“WESCO Common Stock”), and adopted a stockholder rights plan, as set forth in the Rights Agreement, dated as of July 17, 2020 (the “Rights Agreement”), by and between WESCO and Computershare Trust Company, N.A., as rights agent. In general terms, the Rights Agreement works by imposing a significant penalty upon any person or group which acquires 10% or more (15% or more in the case of passive investors filing statements on Schedule 13G) of the outstanding WESCO Common Stock without the approval of the Board. The dividend Right was paid on July 27, 2020 to WESCO stockholders of record as of the close of business on July 27, 2020. The Rights Agreement provides that the Rights will expire on July 16, 2021. The Rights have no value upon issuance.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
INCOME TAXES	12. INCOME TAXES Pursuant to the enactment of the Tax Cuts and Jobs Act of 2017 (the "TCJA”) on December 22, 2017, the Company recognized the provisional income tax effects of the TCJA in the year ended December 31, 2017. 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 liability for the one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax") based upon guidance issued by the Internal Revenue Service ("IRS"), which resulted in a discrete benefit of $3.7 million. As of December 31, 2020 and 2019, a liability of $63.3 million and $36.8 million, respectively, was recorded as components of other current and noncurrent liabilities in the Consolidated Balance Sheets for the transition tax. The transition tax will be paid in installments. The accounting for the income tax effects of the TCJA is complete 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, 2020 2019 2018 (In thousands) United States $ 26,031 $ 198,566 $ 198,556 Foreign 96,811 83,495 82,469 Income before income taxes $ 122,842 $ 282,061 $ 281,025 The following table sets forth the components of the provision (benefit) for income taxes: Year Ended December 31, 2020 2019 2018 (In thousands) Current income taxes: Federal $ 25,605 $ 31,695 $ 28,464 State 11,322 8,616 7,458 Foreign 19,414 6,347 10,611 Total current income taxes 56,341 46,658 46,533 Deferred income taxes: Federal (17,913) 6,774 5,253 State (7,264) 1,846 1,967 Foreign (8,361) 4,585 1,917 Total deferred income taxes (33,538) 13,205 9,137 Provision for income taxes $ 22,803 $ 59,863 $ 55,670 The following table sets forth the reconciliation between the federal statutory income tax rate and the effective tax rate: Year Ended December 31, 2020 2019 2018 Federal statutory rate 21.0 % 21.0 % 21.0 % State income taxes, net of federal income tax benefit 1.4 3.1 2.8 Deemed repatriation of undistributed foreign earnings — (1.3) (1.2) Deferred income tax remeasurement — — (0.3) Tax effect of intercompany financing (13.4) (5.5) (5.6) Unrecognized tax benefits 2.1 (0.4) (0.1) Nondeductible expenses 5.7 0.7 1.0 Change in valuation allowance 1.8 0.6 0.6 Other — 3.0 1.6 Effective tax rate 18.6 % 21.2 % 19.8 % Undistributed earnings of the Company's foreign subsidiaries amounted to approximately $1,835.0 million at December 31, 2020. Most of these earnings have been taxed in the U.S. under either the one-time transition tax or the GILTI tax regime imposed by the TCJA. Except for a portion of foreign earnings previously taxed in the U.S. that can effectively be distributed without further material U.S. or foreign taxation, the Company continues to assert that the undistributed earnings of its foreign subsidiaries are indefinitely reinvested. To the extent the earnings of the Company's foreign subsidiaries are distributed in the form of dividends, such earnings may be subject to additional taxes. WESCO estimates that additional taxes of approximately $75.0 million would be payable upon the remittance of foreign earnings as dividends at December 31, 2020, based upon the laws in effect on that date. The Company believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without incurring any material tax cost to repatriate cash held by its foreign subsidiaries. The following table sets forth deferred tax assets and liabilities: As of December 31, 2020 2019 (In thousands) Assets Liabilities Assets Liabilities Accounts receivable $ 17,560 $ — $ 3,382 $ — Inventories 14,793 — — 4,580 Depreciation of property, buildings and equipment — 60,687 — 18,393 Operating leases 134,377 136,477 61,326 60,670 Amortization of intangible assets — 540,520 — 159,573 Employee benefits 53,040 — 20,641 — Stock-based compensation 14,061 — 13,792 — Tax loss carryforwards 36,923 — 10,486 — Foreign tax credit carryforwards 55,637 — 1,247 — Other 27,643 6,286 6,791 3,964 Deferred income taxes before valuation allowance 354,034 743,970 117,665 247,180 Valuation allowance (60,629) — (5,854) — Total deferred income taxes $ 293,405 $ 743,970 $ 111,811 $ 247,180 In connection with the acquisition of Anixter, WESCO recorded deferred income tax liabilities of $347.3 million, which primarily related to identifiable intangible assets for which there was no increase in tax basis. WESCO had deferred tax assets of $34.5 million and $7.9 million as of December 31, 2020 and 2019, respectively, related to foreign net operating loss carryforwards. These net operating loss carryforwards expire beginning in 2021 through 2030, while some may be carried forward indefinitely. The Company determined that certain foreign net operating loss carryforwards would not be realized before they expire. Accordingly, the Company recorded a valuation allowance of $22.3 million and $4.6 million against deferred tax assets related to certain foreign net operating loss carryforwards at December 31, 2020 and 2019, respectively. Additionally, these foreign jurisdictions had deferred tax assets of $8.2 million as of December 31, 2020 related to other future deductible temporary differences. The Company recorded a full valuation allowance against this amount as of December 31, 2020. As of December 31, 2020 and 2019, WESCO had deferred tax assets of $2.4 million and $2.6 million, respectively, related to state net operating loss carryforwards. These carryforwards expire beginning in 2024 through 2039. As of December 31, 2020 and 2019, WESCO had deferred tax assets of $55.6 million and $1.2 million, respectively, related to foreign tax credit carryforwards. The foreign tax credit carryforwards expire beginning in 2026 through 2030. The Company determined that certain foreign tax credit carryforwards will not be realized before they expire. Accordingly, the Company recorded a valuation allowance of $30.1 million and $1.2 million against deferred tax assets related to certain foreign tax credit carryforwards at December 31, 2020 and 2019, respectively. The Company is under examination by tax authorities in various jurisdictions 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 2016 and forward Canada 2012 and forward UK 2015 and forward The following table sets forth the reconciliation of gross unrecognized tax benefits: As of December 31, 2020 2019 2018 (In thousands) Beginning balance January 1 $ 54 $ 1,293 $ 4,348 Additions for current year tax positions 14,009 — — Additions for acquired tax positions 68,048 — — Reductions for prior year tax positions (43) — — Settlements — (1,290) (2,646) Lapse in statute of limitations (15,886) — (287) Foreign currency exchange rate changes 1,893 51 (122) Ending balance December 31 $ 68,075 $ 54 $ 1,293 The total amount of unrecognized tax benefits were $68.1 million and $0.1 million as of December 31, 2020 and 2019, respectively. The amount of unrecognized tax benefits that would affect the effective tax rate if recognized in the consolidated financial statements for the years ended December 31, 2020, 2019 and 2018 were $29.1 million, $0.1 million, and $1.3 million, respectively. Within the next twelve months, the amount of unrecognized tax benefits is expected to decrease by $3.6 million due to the expiration of statutes of limitation. Such change would result in a favorable effective tax rate impact of $4.2 million. The Company classifies interest related to unrecognized tax benefits as a component of net interest in the Consolidated Statement of Income and Comprehensive Income. In 2020, the Company recognized interest expense on unrecognized tax benefits of $0.3 million. The Company recognized interest income on unrecognized tax benefits of $0.8 million in 2019. In 2018, interest expense on unrecognized tax benefits was $0.2 million. As of December 31, 2020 and 2019, WESCO had a liability of $5.5 million and $0.1 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 for 2020, 2019, and 2018 were immaterial. As of December 31, 2020, WESCO had a liability of $1.5 million for penalties related to unrecognized tax benefits.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
EARNINGS PER SHARE	13. EARNINGS PER SHARE Basic earnings per share is computed by dividing net income attributable to common stockholders by the weighted-average number of common shares outstanding during the periods. Diluted earnings per share is computed by dividing net income attributable to common stockholders 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, 2020 2019 2018 (In thousands, except per share data) Net income attributable to WESCO International, Inc. $ 100,560 $ 223,426 $ 227,343 Less: Preferred stock dividends 30,139 — — Net income attributable to common stockholders $ 70,421 $ 223,426 $ 227,343 Weighted-average common shares outstanding used in computing basic earnings per share 46,174 43,104 46,722 Common shares issuable upon exercise of dilutive equity awards 451 383 477 Weighted-average common shares outstanding and common share equivalents used in computing diluted earnings per share 46,625 43,487 47,199 Earnings per share attributable to common stockholders Basic $ 1.53 $ 5.18 $ 4.87 Diluted $ 1.51 $ 5.14 $ 4.82 For the years ended December 31, 2020, 2019 and 2018, the computation of diluted earnings per share attributable to common stockholders excluded equity awards of approximately 1.8 million, 1.7 million and 1.6 million, respectively. These shares were excluded because their effect would have been antidilutive. In December 2017, 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, 2020 (the "Repurchase Authorization"). In October 2018, the Board approved an increase to the 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 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 Repurchase Authorization. In exchange for an up-front cash payment of $150.0 million, the Company received 3,090,312 shares. The Company did not repurchase any shares of its common stock during the year ended December 31, 2020. As of December 31, 2020, WESCO had repurchased 5,459,030 shares of common stock for $275.0 million under the Repurchase Authorization.

EMPLOYEE BENEFIT PLANS

EMPLOYEE BENEFIT PLANS	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Retirement Benefits	14. EMPLOYEE BENEFIT PLANS Defined Contribution Plans WESCO Distribution sponsors a defined contribution retirement savings plan for the majority of its U.S. employees. The Company matches contributions made by employees at an amount equal to 50% of participants' total monthly contributions up to 6% of eligible compensation. Contributions are made in cash and employees have the option to transfer balances allocated to their accounts into any of the available investment options. Due to the COVID-19 pandemic and its adverse effect on WESCO's results of operations, the Company suspended matching employer contributions between April 16, 2020 and September 30, 2020. The Company 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 years ended December 31, 2020 and December 31, 2019. Discretionary employer contribution charges of $20.6 million were incurred in 2018. WESCO Distribution Canada LP, a wholly-owned subsidiary of the Company, sponsors a defined contribution plan for certain Canadian employees. The Company makes contributions in amounts ranging from 3% to 5% of participants' eligible compensation based on years of continuous service. Anixter Inc. sponsors a defined contribution plan covering all of its non-union U.S. employees (the "Anixter Employee Savings Plan"). The employer match for the Anixter Employee Savings Plan is equal to 50% of a participant's contribution up to 5% of the participant's compensation. Anixter Inc. will also make an annual contribution to the Anixter Employee Savings Plan on behalf of each active participant who is hired or rehired on or after July 1, 2015, or is not participating in the Anixter Inc. Pension Plan. The amount of the employer annual contribution is equal to either 2% or 2.5% of the participant’s compensation, as determined by the participant’s years of service. This contribution is in lieu of being eligible for the Anixter Inc. Pension Plan. Certain of Anixter Inc.'s foreign subsidiaries also have defined contribution plans. Contributions to these plans are based upon various levels of employee participation and legal requirements. For the years ended December 31, 2020, 2019 and 2018, WESCO incurred charges of $18.3 million, $22.9 million, and $42.9 million, respectively, for all defined contribution plans. Deferred Compensation Plans WESCO Distribution sponsors a non-qualified deferred compensation plan (the "WESCO Deferred Compensation Plan") that permits select employees to make pre-tax deferrals of salary and bonus. Employees have the option to transfer balances allocated to their accounts in the WESCO Deferred Compensation Plan into any of the available investment options. The WESCO Deferred Compensation Plan is an unfunded plan. As of December 31, 2020, the Company's obligation under the deferred compensation plan was $27.4 million, of which $10.1 million was included in other current liabilities and $17.3 million in other noncurrent liabilities in the Consolidated Balance Sheet. At December 31, 2019, the Company's obligation under the deferred compensation plan was $25.2 million and was included in other noncurrent liabilities in the Consolidated Balance Sheet. Anixter Inc. sponsors a non-qualified deferred compensation plan (the "Anixter Deferred Compensation Plan") that permits select employees to make pre-tax deferrals of salary and bonus. Interest is accrued monthly on the deferred compensation balances based on the average ten-year Treasury note rate for the previous three months times a factor of 1.4, and the rate is further adjusted if certain financial goals are achieved. In the fourth quarter of 2020, the Company made a determination to terminate the Anixter Deferred Compensation Plan. Accordingly, a deferred compensation liability of $45.1 million has been classified in other current liabilities in the Consolidated Balance Sheet at December 31, 2020 as the Company expects to make lump sum payments directly to participants of the plan during 2021. Concurrent with the implementation of the Anixter Deferred Compensation Plan, Anixter established a Rabbi Trust arrangement to provide for the liabilities associated with the deferred compensation plan and an executive non-qualified defined benefit plan. The assets are invested in marketable securities. At December 31, 2020, $39.6 million was recorded in other current assets in the Consolidated Balance Sheet for this arrangement. Defined Benefit Plans WESCO sponsors a contributory defined benefit plan (the "EECOL Plan") covering substantially all Canadian employees of EECOL. The EECOL Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the EECOL Plan. Participants become 100% vested after two years of continuous service or, if earlier, at the participant's normal retirement age. WESCO also sponsors a Supplemental Executive Retirement Plan (the "EECOL SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the EECOL SERP was closed to new participants and existing participants became 100% vested. EECOL SERP participants continue to contribute 4% of their earnings to the EECOL Plan. In connection with the June 22, 2020 acquisition of Anixter discussed in Note 6, "Acquisitions", the Company assumed various defined benefit pension plans sponsored by Anixter Inc. These include defined benefit pension plans in the U.S., which consist of the Anixter Inc. Pension Plan, the Executive Benefit Plan and the Supplemental Executive Retirement Plan (the "Anixter SERP") (together, the "Domestic Plans") and various defined benefit pension plans covering employees of foreign subsidiaries in Canada and Europe (together with the "EECOL Plan" and "EECOL SERP", the "Foreign Plans"). For all defined benefit plans assumed as part of the merger with Anixter, the projected benefit obligation ("PBO") and fair value of plan assets were remeasured as of the acquisition date. The Anixter Inc. Pension Plan was frozen to entrants first hired or rehired on or after July 1, 2015. The majority of the Anixter defined benefit pension plans are non-contributory and, with the exception of the U.S. and Canada, cover substantially all full-time employees in their respective countries. Retirement benefits are provided based on compensation as defined in each of the pension plans. In the fourth quarter of 2020, the Company made a determination to terminate both the Anixter Inc. Executive Benefit Plan and the Anixter SERP. Accordingly, pension liabilities totaling $18.1 million associated with the Anixter Inc. Executive Benefit Plan and the Anixter SERP have been classified as current on the Consolidated Balance Sheet at December 31, 2020 as the Company expects to make lump sum payments directly to participants of these plans during 2021. The Domestic Plans are funded as required by the Employee Retirement Income Security Act of 1974 ("ERISA") and the IRS and all Foreign Plans, including the EECOL Plan and EECOL SERP, are funded as required by applicable foreign laws. The Anixter Inc. Executive Benefit Plan and the Anixter SERP are unfunded plans. The following table presents the changes in benefit obligations, plan assets and funded status for the defined benefit plans: Domestic Plans Foreign Plans Total (In thousands) 2020 2019 2020 2019 (2) 2020 2019 (2) Change in Projected Benefit Obligation Beginning balance $ — $ — $ 134,852 $ 105,515 $ 134,852 $ 105,515 Impact of acquisition (1) 317,893 — 301,206 — 619,099 — Service cost 1,763 — 9,029 4,602 10,792 4,602 Interest cost 4,787 — 7,162 4,362 11,949 4,362 Participant contributions — — 728 736 728 736 Actuarial loss, including assumption changes 12,911 — 14,044 18,591 26,955 18,591 Benefits paid from plan assets (4,222) — (9,008) (4,459) (13,230) (4,459) Benefits paid from Company assets (547) — (448) — (995) — Curtailment (101) — — — (101) — Plan amendment — — (37) — (37) — Settlement — — (1,235) — (1,235) — Foreign currency exchange rate changes — — 30,562 5,505 30,562 5,505 Ending balance $ 332,484 $ — $ 486,855 $ 134,852 $ 819,339 $ 134,852 Change in Plan Assets at Fair Value Beginning balance $ — $ — $ 103,385 $ 86,556 $ 103,385 $ 86,556 Impact of acquisition (1) 324,292 — 218,644 — 542,936 — Actual return on plan assets 35,217 — 23,947 12,763 59,164 12,763 Participant contributions — — 728 736 728 736 Employer contributions — — 6,838 3,198 6,838 3,198 Benefits paid (4,222) — (9,008) (4,459) (13,230) (4,459) Settlement — — (1,235) — (1,235) — Foreign currency exchange rate changes — — 22,419 4,591 22,419 4,591 Ending balance $ 355,287 $ — $ 365,718 $ 103,385 $ 721,005 $ 103,385 Funded Status $ 22,803 $ — $ (121,137) $ (31,467) $ (98,334) $ (31,467) Amounts Recognized in the Consolidated Balance Sheets Other assets $ 40,921 $ — $ 179 $ — $ 41,100 $ — Other current liabilities (18,118) — (471) (383) (18,589) (383) Other noncurrent liabilities — — (120,845) (31,084) (120,845) (31,084) Net amount recognized $ 22,803 $ — $ (121,137) $ (31,467) $ (98,334) $ (31,467) Weighted Average Assumptions Used to Determine Benefit Obligations Discount rate 2.6 % — % 2.0 % 3.2 % 2.2 % 3.2 % Rate of compensation increase 3.8 % — % 3.2 % 3.5 % 3.4 % 3.5 % (1) As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter. (2) For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP. The measurement date for all plans is December 31st. Accordingly, at the end of each fiscal year, the Company determines the discount rate to measure the plan liabilities at their present value. The discount rate reflects the current rate at which the pension liabilities could effectively be settled at the end of the year. In estimating this rate at the end of 2020, the Company reviewed rates of return on relevant market indices and concluded the Willis Towers Watson Global Rate Link Model was consistent with observable market conditions and industry standards for developing spot rate curves. At the end of 2019, the discount rate related to the EECOL Plan and the EECOL SERP was determined using the Canadian Institute of Actuaries methodology. At December 31, 2020 and 2019, the consolidated weighted-average discount rate of all plans was 2.2% and 3.2%, respectively, and these rates were used to measure the PBO at the end of each respective year end. Due primarily to the merger with Anixter, the PBO increased to $819.3 million at December 31, 2020 from $134.9 million at December 31, 2019. The consolidated net unfunded status was $98.3 million at December 31, 2020 compared to $31.5 million at December 31, 2019. The PBO in 2020 was $332.5 million for the Domestic Plans and $486.8 million for the Foreign Plans. The Company had 13 plans in 2020 where the PBO was in excess of the fair value of plan assets. For pension plans with PBO in excess of plan assets the aggregate PBO was $504.8 million, and the aggregate fair value of plan assets was $365.4 million. The PBO in 2019 of $134.9 million related to the EECOL Plan and the EECOL SERP and compared to a fair value of plan assets of $103.4 million. The accumulated benefit obligation in 2020 was $328.2 million for the Domestic Plans and $417.6 million for the Foreign Plans. The Company had 13 plans in 2020 where the accumulated benefit obligation was in excess of the fair value of plan assets. For pension plans with accumulated benefit obligations in excess of plan assets the aggregate pension accumulated benefit obligation was $435.6 million, and the aggregate fair value of plan assets was $365.4 million. The accumulated benefit obligation in 2019 of $104.6 million related to the EECOL Plan and the EECOL SERP and compared to a fair value of plan assets of $103.4 million. The following table presents the components of net periodic pension (benefit) cost: Domestic Plans (1) Foreign Plans (1) Total (In thousands) 2020 2019 2018 2020 2019 2018 2020 2019 2018 Components of Net Periodic Pension (Benefit) Cost Service cost $ 1,763 $ — $ — $ 9,029 $ 4,602 $ 5,242 $ 10,792 $ 4,602 $ 5,242 Interest cost 4,787 — — 7,162 4,362 4,137 11,949 4,362 4,137 Expected return on plan assets (8,395) — — (11,659) (5,695) (5,969) (20,054) (5,695) (5,969) Recognized actuarial gain — — — — (63) (46) — (63) (46) Settlement — — — (144) — — (144) — — Net periodic pension (benefit) cost $ (1,845) $ — $ — $ 4,388 $ 3,206 $ 3,364 $ 2,543 $ 3,206 $ 3,364 (1) As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter. The Company began recognizing the associated net periodic pension (benefit) cost as of the acquisition date. The service cost of $10.8 million, $4.6 million and $5.2 million for the years ended December 31, 2020, 2019 and 2018, respectively, was reported as a component of selling, general and administrative expenses. The other components of net periodic pension (benefit) cost totaling a net benefit of $8.2 million, $1.4 million and $1.9 million for the years ended December 31, 2020, 2019 and 2018, respectively, were presented as a component of other, net. The following weighted-average actuarial assumptions were used to determine net periodic pension (benefit) cost: Domestic Plans (1) Foreign Plans (1) Total 2020 2019 2018 2020 2019 2018 2020 2019 2018 Discount rate 2.9 % — % — % 2.2 % 4.0 % 3.5 % 2.5 % 4.0 % 3.5 % Expected return on plan assets 5.5 % — % — % 5.2 % 6.4 % 6.4 % 5.3 % 6.4 % 6.4 % Rate of compensation increase 3.8 % — % — % 3.4 % 3.8 % 3.8 % 3.5 % 3.8 % 3.8 % (1) As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter. The Company began using the related assumptions as of the acquisition date. The expected long-term rate of return on plan assets reflects the average rate of earnings expected on the invested assets and future assets to be invested to provide for the benefits included in the projected benefit obligation. The Company uses historic plan asset returns combined with current market conditions to estimate the rate of return. The weighted-average expected long-term rate of return on plan assets used in the determination of net periodic pension cost for 2020 was 5.3%. As a result of the combined effect of valuation changes in both the equity and bond markets, the plan assets produced an actual gain of 13.6% in 2020. The difference between the expected return and actual return on plan assets is amortized into expense over the service lives of the plan participants. These amounts are reflected on the balance sheet through charges to accumulated other comprehensive loss, a component of stockholders’ equity. The following table sets forth the changes and the end of year components of accumulated other comprehensive (income) loss for the defined benefit plans: Year Ended December 31, (In thousands) 2020 2019 Changes to Balance: Beginning balance, before tax effect $ 8,890 $ (2,696) Prior service credit arising in current year (37) — Net actuarial (gain) loss arising in current year (12,154) 11,586 Curtailment (101) — Settlement 144 — Foreign currency exchange rate changes 196 — Ending balance, before tax effect $ (3,062) $ 8,890 As of December 31, (In thousands) 2020 2019 Components of Balance: Prior service credit $ (37) $ — Net actuarial (gain) loss (3,025) 8,890 Ending balance, before tax effect (3,062) 8,890 Tax effect 562 (2,329) Ending balance, after tax effect $ (2,500) $ 6,561 The following benefit payments, which reflect expected future service, are expected to be paid as follows: (In thousands) Domestic Plans Foreign Plans Total 2021 $ 28,527 $ 9,873 $ 38,400 2022 11,165 9,978 21,143 2023 12,065 10,613 22,678 2024 13,046 11,145 24,191 2025 13,807 11,988 25,795 2026 to 2030 78,122 83,178 161,300 The Company expects to contribute approximately $11.4 million to its Foreign Plans in 2021. The Company does not expect to make a contribution to its domestic qualified pension plan in 2021 due to its overfunded status. As a result of the termination of its two domestic non-qualified pension plans, the Company estimates that it will make $18.1 million of lump sum payments directly to participants of these plans during 2021. The assets of the various defined benefit plans are held in separate independent trusts and managed by independent third party advisors. The investment objective for the defined benefit plans is to ensure an adequate level of assets is available to fund the benefits owed to employees and their beneficiaries when they become payable. In meeting this objective, the Company seeks to achieve a level of absolute investment return consistent with a prudent level of portfolio risk. The Company's risk preference is to refrain from exposing the plans to higher volatility in pursuit of potential higher returns. The Domestic Plans' and Foreign Plans' asset mixes and the asset allocation guidelines for such plans are summarized as follows: Domestic Plans Allocation Guidelines December 31, 2020 Min Target Max Equities 38.6 % 30 % 37 % 45 % Debt securities: Domestic treasuries 22.2 — 24 40 Corporate bonds 6.7 — 8 40 Other 15.6 9 14 19 Total debt securities 44.5 46 Property/real estate 14.8 9 16 23 Other 2.1 — 1 5 100.0 % 100 % Foreign Plans Allocation Guidelines December 31, 2020 Min Target Max Equities 38.1 % 25 % 41 % 48 % Debt securities: Corporate bonds 5.9 1 1 37 Other 40.6 26 44 65 Total debt securities 46.5 45 Property/real estate 4.8 2 6 8 Insurance products 5.4 5 5 5 Other 5.2 3 3 12 100.0 % 100 % Foreign Plans Allocation Guidelines December 31, 2019 Target Equities: Canadian equities 12.5 % 12.5 % U.S. equities 5.0 5.0 Non-North American equities 22.5 22.5 Total equities 40.0 40.0 Fixed income investments 44.8 45.0 Other 15.2 15.0 100.0 % 100.0 % The pension committees meet regularly to assess investment performance relative to asset allocation guidelines. The Company periodically rebalances its asset portfolios to be in line with its allocation guidelines. For 2020, the Domestic plan investment policy guidelines were as follows: • Each asset class is managed by one or more active and passive investment managers • Each asset class may be invested in a commingled fund, mutual fund, or separately managed account • Investment in Exchange Traded Funds ("ETFs") is permissible • Each manager is expected to be "fully invested" with minimal cash holdings • Derivative instruments such as futures, swaps and options may be used on a limited basis; For funds that employ derivatives, the loss of invested capital to the Trust should be limited to the amount invested in the fund • The equity portfolio is diversified by sector and geography • The real assets portfolio is invested in Real Estate Investment Trusts ("REITs") and private real estate • The fixed income is invested in U.S. Treasuries, investment grade corporate debt (denominated in U.S. dollars), and other credit investments including below investment grade rated bonds and loans, securitized credit, and emerging market debt The investment policies for the Foreign plans are the responsibility of the various trustees. Generally, the investment policy guidelines are as follows: • Make sure that the obligations to the beneficiaries of the plan can be met • Maintain funds at a level to meet the minimum funding requirements • The investment managers are expected to provide a return, within certain tracking tolerances, close to that of the relevant market’s indices The following tables set forth the fair value of the Domestic and Foreign Plans' assets by asset category: December 31, 2020 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Domestic Plans Equities $ — $ — $ — $ 137,098 $ 137,098 Debt securities: Domestic treasuries — — — 78,808 78,808 Corporate bonds — — — 23,824 23,824 Other — — — 55,547 55,547 Property/real estate — — — 52,708 52,708 Insurance products — — — — — Other 7,302 — — — 7,302 Total investments in Domestic Plans $ 7,302 $ — $ — $ 347,985 $ 355,287 Foreign Plans Equities $ — $ — $ — $ 139,537 $ 139,537 Debt securities: Domestic treasuries — — — — — Corporate bonds — — — 21,677 21,677 Other — — — 148,469 148,469 Property/real estate — — — 17,365 17,365 Insurance products — 19,611 — — 19,611 Other 747 — — 18,312 19,059 Total investments in Foreign Plans $ 747 $ 19,611 $ — $ 345,360 $ 365,718 Total Equities $ — $ — $ — $ 276,635 $ 276,635 Debt securities: Domestic treasuries — — — 78,808 78,808 Corporate bonds — — — 45,501 45,501 Other — — — 204,016 204,016 Property/real estate — — — 70,073 70,073 Insurance products — 19,611 — — 19,611 Other 8,049 — — 18,312 26,361 Total investments $ 8,049 $ 19,611 $ — $ 693,345 $ 721,005 (1) 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 table are intended to reconcile the fair value hierarchy to the total fair value of plan assets. December 31, 2019 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Foreign Plans Equities: 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 (1) 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 table are intended to reconcile the fair value hierarchy to the total fair value of plan assets. The Domestic and Foreign Plans' 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 majority of pension assets are comprised of common/collective/pool funds (i.e., mutual funds). These funds 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. Other Benefits As permitted by the Merger Agreement, Anixter granted restricted stock units prior to June 22, 2020 in the ordinary course of business to its employees. These awards, which did not accelerate solely as a result of the Merger, were converted into cash-only settled WESCO phantom stock units, which vest ratably over a 3-year period. As of December 31, 2020, the estimated fair value of these awards was $22.8 million. The Company recognized compensation expense associated with these awards of $9.2 million for the year ended December 31, 2020, which is reported as a component of selling, general and administrative expenses.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2020
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. In connection with the merger with Anixter on June 22, 2020, the Company assumed a portion of the remaining share reserve available under Anixter’s 2017 Stock Incentive Plan. The number of assumed shares, as adjusted, was equal to 185,000 shares and may be used for awards to be granted under the LTIP. 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, 2020, 1.1 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 is determined using the Black-Scholes model. 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. Except for the special award described below, 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. On July 2, 2020, a special award of restricted stock units was granted to certain officers of the Company. These awards vest in tranches of 30% on each of the first and second anniversaries of the grant date and 40% on the third anniversary of the grant date, subject, in each case, to continued employment through the applicable anniversary date. Performance-based awards granted in 2020 and 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. WESCO recognized $19.3 million, $19.1 million and $16.4 million of non-cash stock-based compensation expense, which is included in selling, general and administrative expenses, for the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, there was $33.5 million of total unrecognized compensation expense related to non-vested stock-based compensation arrangements for all awards previously made of which approximately $17.6 million is expected to be recognized in 2021, $12.3 million in 2022 and $3.6 million in 2023. The total intrinsic value of awards exercised during the years ended December 31, 2020, 2019, and 2018 was $8.8 million, $10.7 million, and $8.2 million, respectively. The gross deferred tax benefit associated with the exercise of stock-based awards totaled $2.0 million, $2.5 million, and $2.0 million in 2020, 2019, and 2018, 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, 2020 2019 2018 Awards Weighted-Average Weighted-Average Aggregate Awards Weighted-Average Awards Weighted-Average Beginning of year 2,337,049 $ 59.72 2,351,633 $ 59.26 2,238,607 $ 57.75 Granted 262,091 48.32 213,618 54.63 509,046 62.68 Exercised (391,339) 47.11 (113,099) 35.01 (192,700) 40.74 Canceled (46,245) 65.93 (115,103) 65.27 (203,320) 68.69 End of year 2,161,556 60.48 5.7 $ 39,834 2,337,049 59.72 2,351,633 59.26 Exercisable at end of year 1,630,891 $ 62.72 4.8 $ 26,622 1,723,370 $ 59.00 1,453,932 $ 57.93 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, 2020 2019 2018 Stock-settled stock appreciation rights granted 262,091 213,618 509,046 Risk free interest rate 1.4% 2.5% 2.5% Expected life (in years) 5 5 5 Expected volatility 30% 29% 28% 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 $13.86, $16.36 and $18.38 for the years ended December 31, 2020, 2019 and 2018, 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, 2020 2019 2018 Awards Weighted-Average Awards Weighted-Average Awards Weighted-Average Unvested at beginning of year 363,729 $ 60.00 327,798 $ 57.87 290,054 $ 58.11 Granted 656,717 37.44 192,106 54.13 122,062 62.40 Vested (83,253) 69.17 (136,777) 46.52 (64,166) 67.91 Forfeited (15,698) 56.79 (19,398) 59.62 (20,152) 58.15 Unvested at end of year 921,495 $ 43.15 363,729 $ 60.00 327,798 $ 57.87 The following table sets forth a summary of performance-based awards and related information for the periods presented: Year Ended December 31, 2020 2019 2018 Awards Weighted-Average Awards Weighted-Average Awards Weighted-Average Unvested at beginning of year 195,305 $ 60.24 138,896 $ 59.33 148,508 $ 60.23 Granted 158,756 49.56 126,874 54.64 44,144 62.80 Vested (25,909) 78.04 (25,696) 42.44 — — Forfeited (22,883) 69.39 (44,769) 52.11 (53,756) 64.67 Unvested at end of year 305,269 $ 52.61 195,305 $ 60.24 138,896 $ 59.33 Vesting of the 305,269 shares of performance-based awards in the table above is dependent upon the achievement of certain performance targets, including 132,838 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 152,634 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

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2020
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 $5.5 million term loan and a $1.0 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 $6.7 million as security for WESTEC’s debt facilities. As of December 31, 2020, WESTEC had outstanding indebtedness totaling $5.8 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, 2020. As of December 31, 2020, the Company had $54.1 million in outstanding letters of credit and guarantees.

BUSINESS SEGMENTS

BUSINESS SEGMENTS	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
SEGMENTS AND RELATED INFORMATION	17. BUSINESS SEGMENTS Prior to the completion of its merger with Anixter on June 22, 2020, as described in Note 6, "Acquisitions", WESCO had four operating segments that had been aggregated as one reportable segment. Effective on the date of acquisition, the Company added Anixter as a separate reportable segment for the quarterly period ended June 30, 2020. At the beginning of the third quarter, the Company identified new operating segments organized around three strategic business units consisting of EES, CSS and UBS. These operating segments are equivalent to the Company's reportable segments. The operating segments in the respective periods were determined in accordance with the manner in which WESCO's chief operating decision maker ("CODM") reviewed financial information during those periods. The Company's CODM evaluates the performance of its operating segments based primarily on net sales, income from operations, and total assets. The applicable comparative financial information reported in the Company's previously issued consolidated financial statements f or the years ended December 31, 2019 and 2018 has been recast below to conform to the basis of the new segments. The following is a description of each of the Company's reportable segments and their business activities. Electrical & Electronic Solutions The EES segment supplies a broad range of products and supply chain solutions primarily to the Construction, Industrial and Original Equipment Manufacturer ("OEM") markets. Product categories include a broad range of electrical equipment and supplies, wire and cable, lubricants, pipe, valves, fittings, fasteners, cutting tools, power transmission, and safety products. In addition, OEM customers require a reliable supply of assemblies and components to incorporate into their own products as well as value-added services such as supplier consolidation, design and technical support, just-in-time supply and electronic commerce, and supply chain management. EES includes the “Electrical and Electronic Solutions” business acquired from Anixter and the majority of the legacy WESCO industrial and construction businesses. Communications & Security Solutions The CSS segment supplies products and customized supply chain solutions to customers in a diverse range of industries including technology, finance, telecommunications service providers, transportation, education, government, healthcare and retail. CSS sells these products directly to end users or through various channels including data communications contractors, security, network, professional audio/visual and systems integrators. CSS has a broad product portfolio that includes copper and fiber optic cable and connectivity, access control, video surveillance, intrusion and fire/life safety, cabinets, power, cable management, wireless, professional audio/video, voice and networking switches and other ancillary products. CSS includes the “Network and Security Solutions” business acquired from Anixter and the legacy WESCO data communications and safety businesses. Utility & Broadband Solutions The UBS segment supplies electrical transmission and distribution products, power plant maintenance, repair and operations supplies and smart-grid products, and arranges materials management and procurement outsourcing for the power generation, power transmission and electricity distribution industries. The UBS segment combines the “Utility Power Solutions” business acquired from Anixter, the legacy WESCO utility business, the legacy WESCO broadband business and the legacy WESCO integrated supply business. Corporate expenses are incurred to obtain and coordinate financing, tax, information technology, legal and other related services. The Company also has various corporate assets which are reported in corporate. Segment assets may not include jointly used assets, but segment results include depreciation expense or other allocations related to those assets. Interest expense and other non-operating items are not allocated to the segments or reviewed on a segment basis. Corporate expenses and assets are shown in the tables below to reconcile the reportable segments to the consolidated financial statements. The following table sets forth financial information by reportable segment for the periods presented: (In thousands) Year Ended December 31, 2020 EES CSS UBS Corporate Total Net sales $ 5,479,760 $ 3,323,264 $ 3,522,971 $ — $ 12,325,995 Income from operations 260,207 217,163 231,702 (362,034) 347,038 Depreciation and amortization 35,811 37,765 22,380 25,644 121,600 Capital expenditures 7,081 1,495 12,834 35,261 56,671 Year Ended December 31, 2019 (In thousands) EES CSS UBS Corporate Total Net sales $ 4,860,541 $ 909,496 $ 2,588,880 $ — $ 8,358,917 Income from operations 261,788 43,835 184,931 (144,337) 346,217 Depreciation and amortization 28,569 7,155 13,583 12,800 62,107 Capital expenditures 20,405 3,093 6,460 14,109 44,067 Year Ended December 31, 2018 (In thousands) EES CSS UBS Corporate Total Net sales $ 4,878,836 $ 857,481 $ 2,440,284 $ — $ 8,176,601 Income from operations 289,065 34,592 165,149 (136,366) 352,440 Depreciation and amortization 30,198 7,413 13,447 11,939 62,997 Capital expenditures 7,487 129 2,235 26,359 36,210 The following table sets forth total assets by reportable segment for the periods presented: As of December 31, 2020 (In thousands) EES CSS UBS Corporate (1) Total Total assets $ 3,726,855 $ 4,275,611 $ 2,947,406 $ 930,342 $ 11,880,214 As of December 31, 2019 (In thousands) EES CSS UBS Corporate (1) Total Total assets $ 2,523,481 $ 610,046 $ 1,747,809 $ 136,299 $ 5,017,635 (1) Total assets for Corporate primarily consist of cash and cash equivalents, deferred income taxes, fixed assets and right-of-use assets associated with operating leases. The following table sets forth tangible long-lived assets by geographic area: As of December 31, 2020 2019 (In thousands) United States $ 693,807 $ 315,288 Canada 146,620 95,642 Other International (1) 93,435 6,352 Total $ 933,862 $ 417,282 (1) No individual other international country's tangible long-lived assets are material.

SELECTED QUARTERLY FINANCIAL DA

SELECTED QUARTERLY FINANCIAL DATA	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
SELECTED QUARTERLY FINANCIAL DATA	18. SELECTED QUARTERLY FINANCIAL DATA (unaudited) The following table sets forth selected quarterly financial data for the years ended December 31, 2020 and 2019: (In thousands, except per share data) First Second Third Fourth 2020 Net sales $ 1,968,647 $ 2,086,706 $ 4,141,801 $ 4,128,841 Cost of goods sold (excluding depreciation and amortization) (1) 1,592,249 1,692,931 3,356,259 3,356,890 Gross profit 376,398 393,775 785,542 771,951 Income from operations 60,913 15,270 178,095 92,763 Income (loss) before income taxes 44,441 (45,313) 104,332 19,384 Net income (loss) (1) 34,175 (34,459) 80,038 20,288 Net income (loss) attributable to common stockholders 34,407 (35,782) 66,167 5,632 Basic earnings (loss) per share attributable to common stockholders (2) $ 0.82 $ (0.84) $ 1.32 $ 0.11 Diluted earnings (loss) per share attributable to common stockholders (3) $ 0.82 $ (0.84) $ 1.31 $ 0.11 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 Gross profit 382,496 408,974 400,197 389,794 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 common stockholders 42,369 63,464 64,495 53,098 Basic earnings per share attributable to common stockholders (2) $ 0.94 $ 1.46 $ 1.53 $ 1.27 Diluted earnings per share attributable to common stockholders (3) $ 0.93 $ 1.45 $ 1.52 $ 1.26 (1) An out-of-period adjustment was recorded during the quarter ended December 31, 2020, resulting in an increase of $23.3 million to cost of goods sold and a decrease of $16.7 million to net income, as described in Note 2, "Accounting Policies". (2) 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. (3) 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 EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events [Text Block]	19. SUBSEQUENT EVENTS On January 14, 2021 (the “Redemption Date”), WESCO Distribution, Inc. redeemed its $500 million aggregate principal amount of 5.375% Senior Notes due 2021 (the "2021 Notes") at a redemption price equal to 100% of the principal amount of the 2021 Notes plus accrued interest on the 2021 Notes to, but not including, the Redemption Date. The redemption of the 2021 Notes was funded with borrowings under the Company's accounts receivable securitization and revolving credit facilities. On February 1 and 12, 2021, the Company sold its legacy WESCO Utility and Datacom businesses in Canada, respectively, for cash consideration totaling approximately $52 million. These transactions fulfill the Company’s commitment to divest these businesses in connection with its Consent Agreement with the Canadian Competition Bureau related to the merger with Anixter. The Company expects to use the net proceeds from the divestiture to repay indebtedness.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Schedule II—Valuation and Qualifying Accounts Balance at Charged to Charged to Balance at of period earnings accounts (1) Deductions (2) end of period Allowance for expected credit losses (In thousands) Year Ended December 31, 2020 $ 25,443 $ 11,701 $ 5,160 $ (18,395) $ 23,909 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 (1) For the year ended December 31, 2020, the amount charged to other accounts relates to the acquisition of Anixter. (2) Includes a reduction in the allowance for expected credit losses due to the write-off of accounts receivable. Balance at Charged to Charged to Balance at of period earnings accounts (1) Deductions end of period Allowance for deferred tax assets (In thousands) Year Ended December 31, 2020 $ 5,854 $ 1,900 $ 52,875 $ — $ 60,629 Year Ended December 31, 2019 4,072 1,745 37 — 5,854 Year Ended December 31, 2018 2,518 1,608 (54) — 4,072 (1) For the year ended December 31, 2020, the amount charged to other accounts includes $59.3 million that was recorded in connection with the acquisition of Anixter.

ACCOUNTING POLICIES (Policies)

ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Consolidation	Basis of Presentation 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. At the beginning of the third quarter of 2020, in connection with the acquisition of Anixter, the Company identified new operating segments. These operating segments, which have been organized around three strategic business units, consist of Electrical & Electronic Solutions ("EES"), Communications & Security Solutions ("CSS") and Utility & Broadband Solutions ("UBS"). The Company's operating segments, which are equivalent to its reportable segments, are described further in Note 17, "Business Segments". The applicable comparative financial information reported in the Company's previously issued consolidated financial statements for the years ended December 31, 2019 and 2018 has been recast in this Annual Report on Form 10-K to conform to the basis of the new segments.
Out-of-Period Adjustment	Out-of-Period Adjustment In the fourth quarter of 2020, management determined that the Company’s inventories were overstated by $60.3 million because of a misstatement in inventory cost absorption accounting, which occurred over multiple periods and also impacted inventories acquired in business combinations during those periods. Accordingly, the Consolidated Balance Sheet at December 31, 2020 reflects a reduction to inventories of $60.3 million, an increase to goodwill of $33.9 million and a decrease to deferred income tax liabilities of $12.0 million. The resulting effect of the out-of-period adjustment on the Consolidated Statement of Income and Comprehensive Income for the year ended December 31, 2020 was a $18.9 million increase to cost of goods sold, which decreased net income for the year by $14.4 million. Management concluded that this misstatement is not material to the current period or the financial statements of any previously filed annual or interim periods.
Reclassification, Policy [Policy Text Block]	Reclassifications The Consolidated Balance Sheet as of December 31, 2019, the Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2019 and 2018, and the Consolidated Statements of Cash Flows for the years ended December 31, 2019 and 2018, respectively, include certain reclassifications to previously reported amounts to conform to the current period's presentation.
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 measured as the amount of consideration WESCO expects to receive in exchange for transferring goods or providing 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. However, transfer may occur at a later date depending on the agreed upon terms, such as delivery at the customer's designated location, or based on consignment terms. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. When providing services, sales are recognized over time as control transfers to the customer, which occurs as services are rendered. 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 typically 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.
Cost of Goods and Service	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 $136.7 million at December 31, 2020 and $81.6 million at December 31, 2019. The supplier volume rebate income as a percentage of net sales was 1.1% in 2020, 1.2% in 2019 and 1.3% in 2018.
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 Expected Credit Losses WESCO recognizes expected credit losses resulting from the inability of its customers to make required payments through an allowance account that is measured each reporting date. WESCO estimates credit losses over the life of its trade accounts receivable using a combination of historical loss data, current credit conditions, specific customer circumstances, and reasonable and supportable forecasts of future economic conditions. The allowance for expected credit losses was $23.9 million at December 31, 2020 and $25.4 million at December 31, 2019. The total amount recorded as selling, general and administrative expense related to credit losses was $10.1 million, $7.0 million and $10.9 million for 2020, 2019 and 2018, 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 reduces the carrying value of its inventories at the earlier of identifying an item that is considered to be obsolete or in excess of supply relative to demand, or no movement in the past 15 months. Reserves for excess and obsolete inventories were $28.7 million and $30.7 million at December 31, 2020 and 2019, respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $15.7 million, $10.0 million and $9.7 million for 2020, 2019 and 2018, respectively.
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 two to ten years for furniture, fixtures and equipment. Costs incurred during the application development stage of internally developing software are capitalized and are reported at the lower of unamortized cost or net realizable value. Costs incurred during the preliminary project and post-implementation stages are expensed as incurred. Capitalized costs include external direct costs of materials and services consumed in developing internal-use computer software, payroll and payroll-related costs for employees who are directly associated with and who devote time to the internal-use computer software project and interest costs. Internal-use computer software is amortized using the straight-line method over its estimated useful life, typically three to seven years. 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 $399.2 million net book value of property, buildings and equipment as of December 31, 2020, $144.1 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 800 branches, warehouses and sales offices, 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 developed by management, which are categorized as Level 3 of the fair value hierarchy, related to 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.
Lessee, Leases	Leases 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. Operating lease expense is recognized on a straight-line basis over the lease term. Operating lease assets and liabilities are recognized at the commencement date based on the present value of the future minimum lease payments. Certain leases contain rent escalation clauses that are either fixed or adjusted periodically for inflation or market rates and such clauses are factored into the Company's determination of lease payments. WESCO also has variable lease payments that do not depend on a rate or index, primarily for items such as common area maintenance and real estate taxes, which are recorded as variable expense when incurred. The operating lease asset includes advance payments and excludes incentives and initial direct costs incurred. 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, or terminate early. 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. For most of WESCO’s leases, the discount rate implicit in the lease is not readily determinable. Accordingly, the Company uses its incremental borrowing rate based on the information available at the lease commencement date to discount lease payments to the present value.
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. The Company first assesses qualitative factors, including macroeconomic conditions, industry and market considerations, cost factors, overall financial performance, other relevant events such as changes in key personnel, changes in the composition or carrying amount of the net assets of a reporting unit, and sustained decreases in share price, to determine whether it is more likely than not that the fair value of WESCO's reporting units are less than their carrying values. If the qualitative assessment indicates that the fair values of the Company's reporting units may not exceed their respective carrying values, then WESCO performs a quantitative test for impairment by comparing the fair value of each reporting unit to its carrying value. The Company determines the fair values of its reporting units using a discounted cash flow analysis and consideration of market multiples. The discounted cash flow analysis uses certain assumptions, including expected operating margins supported by a combination of historical results, current forecasts, market data and recent economic events, which are categorized within Level 3 of the fair value hierarchy. The Company uses a discount rate that reflects market participants' cost of capital. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2020 and 2019, goodwill and indefinite-lived trademarks totaled $4.0 billion and $1.9 billion, respectively.
Definite Lived Intangible Assets	Definite Lived Intangible Assets Definite lived intangible assets are amortized over 2 to 20 years. 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. WESCO continually evaluates whether events or circumstances have occurred that would indicate the remaining estimated useful lives of definite lived intangible assets require revision or that the remaining carrying value of such assets may not be recoverable.
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 $27.9 million and $12.9 million at December 31, 2020 and 2019, 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 taxable 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 recognized in the consolidated financial statements. 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 a portion of foreign earnings previously taxed in the U.S. that can effectively be distributed without further material U.S. or foreign taxation, the Company continues to assert that the undistributed earnings of its foreign subsidiaries are indefinitely reinvested. To the extent the earnings of the Company's foreign subsidiaries are distributed in the form of dividends, such earnings may be subject to additional taxes. The Company believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without incurring any material tax cost to repatriate cash held by its foreign subsidiaries. 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.
Foreign Currency	Foreign Currency The local currency is the functional currency for most of the Company's operations outside the U.S. 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.
Pension and Other Postretirement Plans, Pensions, Policy [Policy Text Block]	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). Unrealized gains and losses related to the Company's defined benefit pension obligations are recognized as a component of other comprehensive income (loss) within stockholders' equity.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company measures the fair value of assets and liabilities on a recurring and nonrecurring basis 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). The Company measures the fair values of goodwill, intangible assets and property, buildings and equipment on a nonrecurring basis if required by impairment tests applicable to these assets, as described above.
Other Income and Expense	Other, net Other non-operating income and expenses ("other, net") primarily includes the non-service cost components of net periodic pension cost (benefit) and foreign exchange gains and losses.
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, "Leases". 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 introduced new guidance for the accounting for credit losses on certain financial instruments. The Company adopted this ASU effective January 1, 2020. The adoption of this new credit loss guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein, and WESCO does not expect it to have a material impact on its financial position or results of operation on an ongoing basis. 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 Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract , which aligned the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The standard was effective for fiscal years beginning after December 15, 2019. The Company adopted this ASU in the first quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein. 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. The Company adopted this ASU in the fourth quarter of 2020. The adoption of this guidance did not have a material impact on the consolidated financial statements and notes thereto presented herein.
New Accounting Pronouncements, Policy	Recently Issued Accounting Pronouncements 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. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting , which provides optional guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in this Update are effective for all entities as of March 12, 2020 through December 31, 2022. Management is currently evaluating the impact related to the replacement of London Interbank Offered Rate (LIBOR) and whether the Company will elect the adoption of the optional guidance. 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 (Tables)

REVENUE (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	The following tables disaggregate WESCO’s net sales by segment and geography for the periods presented: Year Ended December 31, (In thousands) 2020 2019 2018 Electrical & Electronic Solutions $ 5,479,760 $ 4,860,541 $ 4,878,836 Communications & Security Solutions 3,323,264 909,496 857,481 Utility & Broadband Solutions 3,522,971 2,588,880 2,440,284 Total by segment $ 12,325,995 $ 8,358,917 $ 8,176,601 Year Ended December 31, (In thousands) 2020 2019 2018 United States $ 9,110,453 $ 6,234,119 $ 6,089,130 Canada 1,892,321 1,647,066 1,647,933 Other International (1) 1,323,221 477,732 439,538 Total by geography (2) $ 12,325,995 $ 8,358,917 $ 8,176,601 (1) No individual other international country's net sales are material. (2) WESCO attributes revenues from external customers to individual countries on the basis of point of sale.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 EES CSS UBS Total (In thousands) Beginning balance January 1, 2020 $ 573,447 $ 235,711 $ 949,882 $ 1,759,040 Adjustments to goodwill for acquisitions (Note 6) (1) (2) (3) (4) 264,538 868,936 250,553 1,384,027 Foreign currency exchange rate changes 15,471 10,853 17,778 44,102 Ending balance December 31, 2020 (4) $ 853,456 $ 1,115,500 $ 1,218,213 $ 3,187,169 (1) Adjustments to goodwill include the final allocation of the purchase price paid for SLS, which is reflected in the EES segment. (2) Adjustments to goodwill include an increase of $33.9 million resulting from the out-of-period adjustment related to inventory cost absorption accounting, as described in Note 2, "Accounting Policies", which affected the EES, CSS and UBS segments by $20.2 million, $2.0 million, and $11.7 million, respectively. (3) The effect of the merger with Anixter on the Company's reportable segments is disclosed in Note 17, "Business Segments". (4) Adjustments to goodwill include $26.1 million that is classified as held for sale on the UBS segment , as disclosed in Note 7, "Assets and Liabilities Held for Sale". Year Ended December 31, 2019 EES CSS UBS Total (In thousands) Beginning balance January 1, 2019 $ 542,704 $ 234,449 $ 945,450 $ 1,722,603 Adjustments to goodwill for acquisitions (Note 6) 5,767 — — 5,767 Foreign currency exchange rate changes 24,976 1,262 4,432 30,670 Ending balance December 31, 2019 $ 573,447 $ 235,711 $ 949,882 $ 1,759,040
Schedule of Intangible Assets by Major Class	The components of intangible assets are as follows: December 31, 2020 December 31, 2019 Life (in years) Gross Carrying Amount (1) Accumulated Amortization (1) Net Gross Carrying Amount (1) Accumulated Amortization (1) Net (In thousands) Intangible assets: Trademarks Indefinite $ 833,793 $ — $ 833,793 $ 98,699 $ — $ 98,699 Customer relationships (2) 10 - 20 1,434,554 (227,585) 1,206,969 358,341 (201,962) 156,379 Distribution agreements (2) 10 - 19 29,212 (21,040) 8,172 37,371 (25,294) 12,077 Trademarks (2) 10 - 15 24,898 (11,415) 13,483 24,800 (9,319) 15,481 Non-compete agreements 2 - 5 4,462 (1,384) 3,078 196 (180) 16 Patents 10 — — — 48,310 (43,687) 4,623 $ 2,326,919 $ (261,424) $ 2,065,495 $ 567,717 $ (280,442) $ 287,275 (1) Excludes the original cost and related accumulated amortization of fully-amortized intangible assets. (2) The net carrying amount as of December 31, 2020 excludes $1.0 million of trademarks, $3.3 million of customer relationships and $1.4 million of distribution agreements that are classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale".
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) 2021 $ 86,619 2022 83,628 2023 81,400 2024 80,087 2025 76,829 Thereafter 823,139

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	12 Months Ended
	Dec. 31, 2020
Business Acquisition [Line Items]
Business Acquisition, Schedule of Consideration Transferred	The total preliminary estimated fair value of consideration transferred for the Merger consisted of the following: (In thousands) Cash portion attributable to common stock outstanding $ 2,476,010 Cash portion attributable to options and restricted stock units outstanding 87,375 Fair value of cash consideration 2,563,385 Common stock consideration 313,512 Series A preferred stock consideration 573,786 Fair value of equity consideration 887,298 Extinguishment of Anixter obligations, including accrued and unpaid interest 1,247,653 Total purchase consideration $ 4,698,336 Supplemental cash flow disclosure related to acquisitions: Cash paid for acquisition $ 3,811,038 Less: Cash acquired (103,463) Cash paid for acquisition, net of cash acquired $ 3,707,575
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table sets forth the preliminary allocation of the purchase consideration to the respective fair value of assets acquired and liabilities assumed for the acquisition of Anixter: (In thousands) Assets Cash and cash equivalents $ 103,463 Trade accounts receivable 1,306,900 Other accounts receivable 116,386 Inventories 1,416,582 Prepaid expenses and other current assets 54,978 Property, buildings and equipment 211,721 Operating lease assets 280,285 Intangible assets 1,838,065 Goodwill 1,370,396 Other assets 139,760 Total assets $ 6,838,536 Liabilities Accounts payable $ 920,163 Accrued payroll and benefit costs 69,480 Short-term debt and current portion of long-term debt 13,225 Other current liabilities 222,119 Long-term debt 77,617 Operating lease liabilities 217,303 Deferred income taxes 374,734 Other noncurrent liabilities 245,559 Total liabilities $ 2,140,200 Fair value of net assets acquired, including goodwill and intangible assets $ 4,698,336
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination	The following table sets forth the preliminary identifiable intangible assets and their estimated weighted-average useful lives: Identifiable Intangible Assets Estimated Weighted-Average Estimated Useful Life in Years (1) (In thousands) Customer relationships $ 1,098,900 19 Trademarks 735,000 Indefinite Non-compete agreements 4,165 2 Total identifiable intangible assets $ 1,838,065 (1) Measurement period adjustments include an update to the estimated useful lives initially assigned to customer relationships, which resulted in income of $6.4 million during the year ended December 31, 2020.
Business Acquisition, Pro Forma Information	Pro Forma Financial Information The following unaudited pro forma financial information presents combined results of operations for the periods presented, as if the Company had completed the Merger on January 1, 2019. The unaudited pro forma financial information includes adjustments to amortization and depreciation for intangible assets and property, buildings and equipment, adjustments to interest expense for the additional indebtedness incurred to complete the acquisition (including the amortization of debt discount and issuance costs), transaction costs, change in control and severance costs, dividends accrued on the Series A preferred stock, compensation expense associated with the WESCO phantom stock unit awards described in Note 14, "Employee Benefit Plans", as well as the respective income tax effects of such adjustments. For the year ended December 31, 2020, adjustments totaling $7.0 million increased the unaudited pro forma net income attributable to common stockholders, and adjustments totaling $201.3 million decreased the unaudited pro forma net income attributable to common stockholders for the year ended December 31, 2019. The unaudited pro forma financial information does not reflect any cost savings, operating synergies or revenue enhancements that WESCO may achieve as a result of its acquisition of Anixter, the costs to integrate the operations of WESCO and Anixter or the costs necessary to achieve these cost savings, operating synergies and revenue enhancements. The unaudited pro forma financial information presented below is not necessarily indicative of consolidated results of operations of the combined business had the acquisition occurred at the beginning of the respective fiscal years, nor is it necessarily indicative of future results of operations of the combined company. Year Ended (In thousands) December 31, 2020 December 31, 2019 Pro forma net sales $ 16,016,902 $ 17,204,472 Pro forma net income attributable to common stockholders 119,839 285,100

ASSETS AND LIABILITIES HELD F_2

ASSETS AND LIABILITIES HELD FOR SALE (Tables)	12 Months Ended
	Dec. 31, 2020
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations	The assets and liabilities classified as held for sale were as follows: As of December 31, 2020 (In thousands) Trade accounts receivable, net $ 4,258 Inventories 16,438 Prepaid expenses and other current assets 395 Property, buildings and equipment, net 263 Operating lease assets 1,938 Intangible assets, net 5,722 Goodwill 26,059 Total assets held for sale $ 55,073 Accounts payable $ 3,639 Other current liabilities 541 Operating lease liabilities 1,537 Total liabilities held for sale $ 5,717

PROPERTY, BUILDINGS AND EQUIP_2

PROPERTY, BUILDINGS AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 (1) 2019 (In thousands) Buildings and leasehold improvements $ 169,873 $ 110,056 Furniture, fixtures and equipment 266,317 162,029 Software costs 235,666 127,919 671,856 400,004 Accumulated depreciation and amortization (312,106) (268,415) 359,750 131,589 Land 26,409 24,106 Construction in progress 12,998 25,753 $ 399,157 $ 181,448 (1) The components of property, buildings and equipment as of December 31, 2020 exclude a total of $0.3 million that is classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Lessee, Operating Lease, Disclosure	The following table sets forth supplemental balance sheet information related to operating leases for the periods presented: As of December 31, (In thousands) 2020 (1) 2019 Operating lease assets $ 534,705 $ 235,834 Current operating lease liabilities (2) 128,322 62,046 Noncurrent operating lease liabilities 414,889 179,830 Total operating lease liabilities $ 543,211 $ 241,876 (1) Operating lease assets and liabilities of $1.9 million and $2.1 million, respectively, are classified as held for sale as of December 31, 2020, as disclosed in Note 7, "Assets and Liabilities Held for Sale". (2) Current operating lease liabilities are recorded as a component of other current liabilities in the Consolidated Balance Sheets.
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 periods presented: Year Ended December 31, (In thousands) 2020 2019 Operating lease cost $ 127,725 $ 73,613 Short-term lease cost 494 90 Variable lease cost 36,230 23,385 Total lease cost $ 164,449 $ 97,088
Schedule of Cash Flow, Supplemental Disclosures	The following table sets forth supplemental cash flow information related to operating leases for the periods presented: Year Ended December 31, (In thousands) 2020 2019 Operating cash flows from operating leases $ 117,106 $ 75,775 Right-of-use assets obtained in exchange for new operating lease liabilities 121,207 60,586
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	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 Consolidated Balance Sheet as of December 31, 2020: (In thousands) 2021 $ 155,071 2022 127,851 2023 100,746 2024 72,847 2025 46,730 Thereafter 124,127 Total undiscounted operating lease payments 627,372 Less: imputed interest (84,161) Total operating lease liabilities $ 543,211

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Instrument [Line Items]
Schedule of Debt	The following table sets forth WESCO’s outstanding indebtedness: As of December 31, 2020 2019 (In thousands) International lines of credit $ 29,575 $ 26,255 Accounts Receivable Securitization Facility 950,000 415,000 Revolving Credit Facility 250,000 — 5.375% Senior Notes due 2021 500,000 500,000 5.50% Senior Notes due 2023 58,636 — 5.375% Senior Notes due 2024 350,000 350,000 6.00% Senior Notes due 2025 4,173 — 7.125% Senior Notes due 2025 1,500,000 — 7.250% Senior Notes due 2028, less debt discount of $9,332 1,315,668 — Finance lease obligations 17,931 1,373 Total debt 4,975,983 1,292,628 Plus: Fair value adjustment to the Anixter Senior Notes 1,650 — Less: Unamortized debt issuance costs (78,850) (8,876) Less: Short-term debt and current portion of long-term debt (528,830) (26,685) Total long-term debt $ 4,369,953 $ 1,257,067
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, 2020: (In thousands) 2021 $ 529,869 2022 4,051 2023 1,016,322 2024 352,183 2025 1,756,055 Thereafter 1,326,835 Total payments on debt $ 4,985,315 Debt discount (9,332) Total debt $ 4,975,983

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
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, 2020 2019 2018 (In thousands) United States $ 26,031 $ 198,566 $ 198,556 Foreign 96,811 83,495 82,469 Income before income taxes $ 122,842 $ 282,061 $ 281,025
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, 2020 2019 2018 (In thousands) Current income taxes: Federal $ 25,605 $ 31,695 $ 28,464 State 11,322 8,616 7,458 Foreign 19,414 6,347 10,611 Total current income taxes 56,341 46,658 46,533 Deferred income taxes: Federal (17,913) 6,774 5,253 State (7,264) 1,846 1,967 Foreign (8,361) 4,585 1,917 Total deferred income taxes (33,538) 13,205 9,137 Provision for income taxes $ 22,803 $ 59,863 $ 55,670
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, 2020 2019 2018 Federal statutory rate 21.0 % 21.0 % 21.0 % State income taxes, net of federal income tax benefit 1.4 3.1 2.8 Deemed repatriation of undistributed foreign earnings — (1.3) (1.2) Deferred income tax remeasurement — — (0.3) Tax effect of intercompany financing (13.4) (5.5) (5.6) Unrecognized tax benefits 2.1 (0.4) (0.1) Nondeductible expenses 5.7 0.7 1.0 Change in valuation allowance 1.8 0.6 0.6 Other — 3.0 1.6 Effective tax rate 18.6 % 21.2 % 19.8 %
Schedule of Deferred Tax Assets and Liabilities	The following table sets forth deferred tax assets and liabilities: As of December 31, 2020 2019 (In thousands) Assets Liabilities Assets Liabilities Accounts receivable $ 17,560 $ — $ 3,382 $ — Inventories 14,793 — — 4,580 Depreciation of property, buildings and equipment — 60,687 — 18,393 Operating leases 134,377 136,477 61,326 60,670 Amortization of intangible assets — 540,520 — 159,573 Employee benefits 53,040 — 20,641 — Stock-based compensation 14,061 — 13,792 — Tax loss carryforwards 36,923 — 10,486 — Foreign tax credit carryforwards 55,637 — 1,247 — Other 27,643 6,286 6,791 3,964 Deferred income taxes before valuation allowance 354,034 743,970 117,665 247,180 Valuation allowance (60,629) — (5,854) — Total deferred income taxes $ 293,405 $ 743,970 $ 111,811 $ 247,180
Summary of Income Tax Examinations	The Company is under examination by tax authorities in various jurisdictions 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 2016 and forward Canada 2012 and forward UK 2015 and forward
Summary of Income Tax Contingencies	The following table sets forth the reconciliation of gross unrecognized tax benefits: As of December 31, 2020 2019 2018 (In thousands) Beginning balance January 1 $ 54 $ 1,293 $ 4,348 Additions for current year tax positions 14,009 — — Additions for acquired tax positions 68,048 — — Reductions for prior year tax positions (43) — — Settlements — (1,290) (2,646) Lapse in statute of limitations (15,886) — (287) Foreign currency exchange rate changes 1,893 51 (122) Ending balance December 31 $ 68,075 $ 54 $ 1,293

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the details of basic and diluted earnings per share: Year Ended December 31, 2020 2019 2018 (In thousands, except per share data) Net income attributable to WESCO International, Inc. $ 100,560 $ 223,426 $ 227,343 Less: Preferred stock dividends 30,139 — — Net income attributable to common stockholders $ 70,421 $ 223,426 $ 227,343 Weighted-average common shares outstanding used in computing basic earnings per share 46,174 43,104 46,722 Common shares issuable upon exercise of dilutive equity awards 451 383 477 Weighted-average common shares outstanding and common share equivalents used in computing diluted earnings per share 46,625 43,487 47,199 Earnings per share attributable to common stockholders Basic $ 1.53 $ 5.18 $ 4.87 Diluted $ 1.51 $ 5.14 $ 4.82

EMPLOYEE BENEFIT PLANS - (Table

EMPLOYEE BENEFIT PLANS - (Tables)	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Schedule of Net Funded Status [Table Text Block]	The following table presents the changes in benefit obligations, plan assets and funded status for the defined benefit plans: Domestic Plans Foreign Plans Total (In thousands) 2020 2019 2020 2019 (2) 2020 2019 (2) Change in Projected Benefit Obligation Beginning balance $ — $ — $ 134,852 $ 105,515 $ 134,852 $ 105,515 Impact of acquisition (1) 317,893 — 301,206 — 619,099 — Service cost 1,763 — 9,029 4,602 10,792 4,602 Interest cost 4,787 — 7,162 4,362 11,949 4,362 Participant contributions — — 728 736 728 736 Actuarial loss, including assumption changes 12,911 — 14,044 18,591 26,955 18,591 Benefits paid from plan assets (4,222) — (9,008) (4,459) (13,230) (4,459) Benefits paid from Company assets (547) — (448) — (995) — Curtailment (101) — — — (101) — Plan amendment — — (37) — (37) — Settlement — — (1,235) — (1,235) — Foreign currency exchange rate changes — — 30,562 5,505 30,562 5,505 Ending balance $ 332,484 $ — $ 486,855 $ 134,852 $ 819,339 $ 134,852 Change in Plan Assets at Fair Value Beginning balance $ — $ — $ 103,385 $ 86,556 $ 103,385 $ 86,556 Impact of acquisition (1) 324,292 — 218,644 — 542,936 — Actual return on plan assets 35,217 — 23,947 12,763 59,164 12,763 Participant contributions — — 728 736 728 736 Employer contributions — — 6,838 3,198 6,838 3,198 Benefits paid (4,222) — (9,008) (4,459) (13,230) (4,459) Settlement — — (1,235) — (1,235) — Foreign currency exchange rate changes — — 22,419 4,591 22,419 4,591 Ending balance $ 355,287 $ — $ 365,718 $ 103,385 $ 721,005 $ 103,385 Funded Status $ 22,803 $ — $ (121,137) $ (31,467) $ (98,334) $ (31,467) Amounts Recognized in the Consolidated Balance Sheets Other assets $ 40,921 $ — $ 179 $ — $ 41,100 $ — Other current liabilities (18,118) — (471) (383) (18,589) (383) Other noncurrent liabilities — — (120,845) (31,084) (120,845) (31,084) Net amount recognized $ 22,803 $ — $ (121,137) $ (31,467) $ (98,334) $ (31,467) Weighted Average Assumptions Used to Determine Benefit Obligations Discount rate 2.6 % — % 2.0 % 3.2 % 2.2 % 3.2 % Rate of compensation increase 3.8 % — % 3.2 % 3.5 % 3.4 % 3.5 % (1) As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter. (2) For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP.
Schedule of Net Benefit Costs [Table Text Block]	The following table presents the components of net periodic pension (benefit) cost: Domestic Plans (1) Foreign Plans (1) Total (In thousands) 2020 2019 2018 2020 2019 2018 2020 2019 2018 Components of Net Periodic Pension (Benefit) Cost Service cost $ 1,763 $ — $ — $ 9,029 $ 4,602 $ 5,242 $ 10,792 $ 4,602 $ 5,242 Interest cost 4,787 — — 7,162 4,362 4,137 11,949 4,362 4,137 Expected return on plan assets (8,395) — — (11,659) (5,695) (5,969) (20,054) (5,695) (5,969) Recognized actuarial gain — — — — (63) (46) — (63) (46) Settlement — — — (144) — — (144) — — Net periodic pension (benefit) cost $ (1,845) $ — $ — $ 4,388 $ 3,206 $ 3,364 $ 2,543 $ 3,206 $ 3,364 (1) As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter. The Company began recognizing the associated net periodic pension (benefit) cost as of the acquisition date.
Defined Benefit Plan, Assumptions [Table Text Block]	The following weighted-average actuarial assumptions were used to determine net periodic pension (benefit) cost: Domestic Plans (1) Foreign Plans (1) Total 2020 2019 2018 2020 2019 2018 2020 2019 2018 Discount rate 2.9 % — % — % 2.2 % 4.0 % 3.5 % 2.5 % 4.0 % 3.5 % Expected return on plan assets 5.5 % — % — % 5.2 % 6.4 % 6.4 % 5.3 % 6.4 % 6.4 % Rate of compensation increase 3.8 % — % — % 3.4 % 3.8 % 3.8 % 3.5 % 3.8 % 3.8 % (1) As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter. The Company began using the related assumptions as of the acquisition date.
Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)	The following table sets forth the changes and the end of year components of accumulated other comprehensive (income) loss for the defined benefit plans: Year Ended December 31, (In thousands) 2020 2019 Changes to Balance: Beginning balance, before tax effect $ 8,890 $ (2,696) Prior service credit arising in current year (37) — Net actuarial (gain) loss arising in current year (12,154) 11,586 Curtailment (101) — Settlement 144 — Foreign currency exchange rate changes 196 — Ending balance, before tax effect $ (3,062) $ 8,890 As of December 31, (In thousands) 2020 2019 Components of Balance: Prior service credit $ (37) $ — Net actuarial (gain) loss (3,025) 8,890 Ending balance, before tax effect (3,062) 8,890 Tax effect 562 (2,329) Ending balance, after tax effect $ (2,500) $ 6,561
Schedule of Expected Benefit Payments [Table Text Block]	The following benefit payments, which reflect expected future service, are expected to be paid as follows: (In thousands) Domestic Plans Foreign Plans Total 2021 $ 28,527 $ 9,873 $ 38,400 2022 11,165 9,978 21,143 2023 12,065 10,613 22,678 2024 13,046 11,145 24,191 2025 13,807 11,988 25,795 2026 to 2030 78,122 83,178 161,300
Defined Benefit Plan, Plan Assets, Allocation [Table Text Block]	The Domestic Plans' and Foreign Plans' asset mixes and the asset allocation guidelines for such plans are summarized as follows: Domestic Plans Allocation Guidelines December 31, 2020 Min Target Max Equities 38.6 % 30 % 37 % 45 % Debt securities: Domestic treasuries 22.2 — 24 40 Corporate bonds 6.7 — 8 40 Other 15.6 9 14 19 Total debt securities 44.5 46 Property/real estate 14.8 9 16 23 Other 2.1 — 1 5 100.0 % 100 % Foreign Plans Allocation Guidelines December 31, 2020 Min Target Max Equities 38.1 % 25 % 41 % 48 % Debt securities: Corporate bonds 5.9 1 1 37 Other 40.6 26 44 65 Total debt securities 46.5 45 Property/real estate 4.8 2 6 8 Insurance products 5.4 5 5 5 Other 5.2 3 3 12 100.0 % 100 % Foreign Plans Allocation Guidelines December 31, 2019 Target Equities: Canadian equities 12.5 % 12.5 % U.S. equities 5.0 5.0 Non-North American equities 22.5 22.5 Total equities 40.0 40.0 Fixed income investments 44.8 45.0 Other 15.2 15.0 100.0 % 100.0 %
Fair Value, Assets Measured on Recurring Basis [Table Text Block]	The following tables set forth the fair value of the Domestic and Foreign Plans' assets by asset category: December 31, 2020 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Domestic Plans Equities $ — $ — $ — $ 137,098 $ 137,098 Debt securities: Domestic treasuries — — — 78,808 78,808 Corporate bonds — — — 23,824 23,824 Other — — — 55,547 55,547 Property/real estate — — — 52,708 52,708 Insurance products — — — — — Other 7,302 — — — 7,302 Total investments in Domestic Plans $ 7,302 $ — $ — $ 347,985 $ 355,287 Foreign Plans Equities $ — $ — $ — $ 139,537 $ 139,537 Debt securities: Domestic treasuries — — — — — Corporate bonds — — — 21,677 21,677 Other — — — 148,469 148,469 Property/real estate — — — 17,365 17,365 Insurance products — 19,611 — — 19,611 Other 747 — — 18,312 19,059 Total investments in Foreign Plans $ 747 $ 19,611 $ — $ 345,360 $ 365,718 Total Equities $ — $ — $ — $ 276,635 $ 276,635 Debt securities: Domestic treasuries — — — 78,808 78,808 Corporate bonds — — — 45,501 45,501 Other — — — 204,016 204,016 Property/real estate — — — 70,073 70,073 Insurance products — 19,611 — — 19,611 Other 8,049 — — 18,312 26,361 Total investments $ 8,049 $ 19,611 $ — $ 693,345 $ 721,005 (1) 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 table are intended to reconcile the fair value hierarchy to the total fair value of plan assets. December 31, 2019 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Foreign Plans Equities: 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 (1) 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 table are intended to reconcile the fair value hierarchy to the total fair value of plan assets.

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 2018 Awards Weighted-Average Weighted-Average Aggregate Awards Weighted-Average Awards Weighted-Average Beginning of year 2,337,049 $ 59.72 2,351,633 $ 59.26 2,238,607 $ 57.75 Granted 262,091 48.32 213,618 54.63 509,046 62.68 Exercised (391,339) 47.11 (113,099) 35.01 (192,700) 40.74 Canceled (46,245) 65.93 (115,103) 65.27 (203,320) 68.69 End of year 2,161,556 60.48 5.7 $ 39,834 2,337,049 59.72 2,351,633 59.26 Exercisable at end of year 1,630,891 $ 62.72 4.8 $ 26,622 1,723,370 $ 59.00 1,453,932 $ 57.93
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, 2020 2019 2018 Stock-settled stock appreciation rights granted 262,091 213,618 509,046 Risk free interest rate 1.4% 2.5% 2.5% Expected life (in years) 5 5 5 Expected volatility 30% 29% 28%
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	The following table sets forth a summary of time-based restricted stock units and related information for the periods presented: Year Ended December 31, 2020 2019 2018 Awards Weighted-Average Awards Weighted-Average Awards Weighted-Average Unvested at beginning of year 363,729 $ 60.00 327,798 $ 57.87 290,054 $ 58.11 Granted 656,717 37.44 192,106 54.13 122,062 62.40 Vested (83,253) 69.17 (136,777) 46.52 (64,166) 67.91 Forfeited (15,698) 56.79 (19,398) 59.62 (20,152) 58.15 Unvested at end of year 921,495 $ 43.15 363,729 $ 60.00 327,798 $ 57.87 The following table sets forth a summary of performance-based awards and related information for the periods presented: Year Ended December 31, 2020 2019 2018 Awards Weighted-Average Awards Weighted-Average Awards Weighted-Average Unvested at beginning of year 195,305 $ 60.24 138,896 $ 59.33 148,508 $ 60.23 Granted 158,756 49.56 126,874 54.64 44,144 62.80 Vested (25,909) 78.04 (25,696) 42.44 — — Forfeited (22,883) 69.39 (44,769) 52.11 (53,756) 64.67 Unvested at end of year 305,269 $ 52.61 195,305 $ 60.24 138,896 $ 59.33

BUSINESS SEGMENTS (Tables)

BUSINESS SEGMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following table sets forth financial information by reportable segment for the periods presented: (In thousands) Year Ended December 31, 2020 EES CSS UBS Corporate Total Net sales $ 5,479,760 $ 3,323,264 $ 3,522,971 $ — $ 12,325,995 Income from operations 260,207 217,163 231,702 (362,034) 347,038 Depreciation and amortization 35,811 37,765 22,380 25,644 121,600 Capital expenditures 7,081 1,495 12,834 35,261 56,671 Year Ended December 31, 2019 (In thousands) EES CSS UBS Corporate Total Net sales $ 4,860,541 $ 909,496 $ 2,588,880 $ — $ 8,358,917 Income from operations 261,788 43,835 184,931 (144,337) 346,217 Depreciation and amortization 28,569 7,155 13,583 12,800 62,107 Capital expenditures 20,405 3,093 6,460 14,109 44,067 Year Ended December 31, 2018 (In thousands) EES CSS UBS Corporate Total Net sales $ 4,878,836 $ 857,481 $ 2,440,284 $ — $ 8,176,601 Income from operations 289,065 34,592 165,149 (136,366) 352,440 Depreciation and amortization 30,198 7,413 13,447 11,939 62,997 Capital expenditures 7,487 129 2,235 26,359 36,210 The following table sets forth total assets by reportable segment for the periods presented: As of December 31, 2020 (In thousands) EES CSS UBS Corporate (1) Total Total assets $ 3,726,855 $ 4,275,611 $ 2,947,406 $ 930,342 $ 11,880,214 As of December 31, 2019 (In thousands) EES CSS UBS Corporate (1) Total Total assets $ 2,523,481 $ 610,046 $ 1,747,809 $ 136,299 $ 5,017,635 (1) Total assets for Corporate primarily consist of cash and cash equivalents, deferred income taxes, fixed assets and right-of-use assets associated with operating leases.
Long-lived Assets by Geographic Areas	The following table sets forth tangible long-lived assets by geographic area: As of December 31, 2020 2019 (In thousands) United States $ 693,807 $ 315,288 Canada 146,620 95,642 Other International (1) 93,435 6,352 Total $ 933,862 $ 417,282 (1) No individual other international country's tangible long-lived assets are material.

SELECTED QUARTERLY FINANCIAL _2

SELECTED QUARTERLY FINANCIAL DATA (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following table sets forth selected quarterly financial data for the years ended December 31, 2020 and 2019: (In thousands, except per share data) First Second Third Fourth 2020 Net sales $ 1,968,647 $ 2,086,706 $ 4,141,801 $ 4,128,841 Cost of goods sold (excluding depreciation and amortization) (1) 1,592,249 1,692,931 3,356,259 3,356,890 Gross profit 376,398 393,775 785,542 771,951 Income from operations 60,913 15,270 178,095 92,763 Income (loss) before income taxes 44,441 (45,313) 104,332 19,384 Net income (loss) (1) 34,175 (34,459) 80,038 20,288 Net income (loss) attributable to common stockholders 34,407 (35,782) 66,167 5,632 Basic earnings (loss) per share attributable to common stockholders (2) $ 0.82 $ (0.84) $ 1.32 $ 0.11 Diluted earnings (loss) per share attributable to common stockholders (3) $ 0.82 $ (0.84) $ 1.31 $ 0.11 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 Gross profit 382,496 408,974 400,197 389,794 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 common stockholders 42,369 63,464 64,495 53,098 Basic earnings per share attributable to common stockholders (2) $ 0.94 $ 1.46 $ 1.53 $ 1.27 Diluted earnings per share attributable to common stockholders (3) $ 0.93 $ 1.45 $ 1.52 $ 1.26 (1) An out-of-period adjustment was recorded during the quarter ended December 31, 2020, resulting in an increase of $23.3 million to cost of goods sold and a decrease of $16.7 million to net income, as described in Note 2, "Accounting Policies". (2) 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. (3) 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.

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Allowance for Doubtful Accounts	Balance at Charged to Charged to Balance at of period earnings accounts (1) Deductions (2) end of period Allowance for expected credit losses (In thousands) Year Ended December 31, 2020 $ 25,443 $ 11,701 $ 5,160 $ (18,395) $ 23,909 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 (1) For the year ended December 31, 2020, the amount charged to other accounts relates to the acquisition of Anixter. (2) Includes a reduction in the allowance for expected credit losses due to the write-off of accounts receivable. Balance at Charged to Charged to Balance at of period earnings accounts (1) Deductions end of period Allowance for deferred tax assets (In thousands) Year Ended December 31, 2020 $ 5,854 $ 1,900 $ 52,875 $ — $ 60,629 Year Ended December 31, 2019 4,072 1,745 37 — 5,854 Year Ended December 31, 2018 2,518 1,608 (54) — 4,072 (1) For the year ended December 31, 2020, the amount charged to other accounts includes $59.3 million that was recorded in connection with the acquisition of Anixter.

ACCOUNTING POLICIES - GENERAL (

ACCOUNTING POLICIES - GENERAL (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Defined Benefit Plan Disclosure
Nontrade Receivables	$ 136,700		$ 136,700		$ 81,600
Accounts Receivable, Allowance for Credit Loss, Current	23,900		23,900		25,400
Accounts Receivable, Credit Loss Expense (Reversal)			10,100		7,000	$ 10,900
Inventory Valuation Reserves	28,700		28,700		30,700
Inventory Write-down			15,700		10,000	$ 9,700
Intangible Assets, Net (Including Goodwill)	4,000,000		4,000,000		1,900,000
Self Insurance Reserve	27,900		27,900		12,900
Operating Lease, Right-of-Use Asset	534,705	[1]	534,705	[1]	235,834		$ 240,000
Operating Lease, Liability	543,211	[1]	543,211	[1]	$ 241,876		$ 245,000
Cost of Goods Sold
Defined Benefit Plan Disclosure
Quantifying Misstatement in Current Year Financial Statements, Amount	23,300		18,900
Net Income
Defined Benefit Plan Disclosure
Quantifying Misstatement in Current Year Financial Statements, Amount	$ 16,700		14,400
Inventories
Defined Benefit Plan Disclosure
Quantifying Misstatement in Current Year Financial Statements, Amount			60,300
Goodwill
Defined Benefit Plan Disclosure
Quantifying Misstatement in Current Year Financial Statements, Amount			33,900
Deferred Income Tax Liability
Defined Benefit Plan Disclosure
Quantifying Misstatement in Current Year Financial Statements, Amount			$ 12,000
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
[1]	Operating lease assets and liabilities of $1.9 million and $2.1 million, respectively, are classified as held for sale as of December 31, 2020, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

ACCOUNTING POLICIES - PPE (Deta

ACCOUNTING POLICIES - PPE (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)branches		Dec. 31, 2019USD ($)
Property, Plant and Equipment [Line Items]
Intangible Assets, Net (Including Goodwill)	$ 4,000,000		$ 1,900,000
Property, buildings and equipment, net	$ 399,157	[1]	$ 181,448
Number of Locations | branches	800
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	two to ten years
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	three to seven years
Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, net	$ 144,100
[1]	The components of property, buildings and equipment as of December 31, 2020 exclude a total of $0.3 million that is classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

REVENUE (Details)

REVENUE (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Net sales		$ 4,128,841	$ 4,141,801	$ 2,086,706	$ 1,968,647	$ 2,099,452	$ 2,148,110	$ 2,150,088	$ 1,961,267	$ 12,325,995	$ 8,358,917	$ 8,176,601
Selling, general and administrative expense										1,859,028	1,173,137	1,151,944
Deferred Revenue		$ 24,300				$ 12,300				24,300	12,300
EES
Disaggregation of Revenue [Line Items]
Net sales										5,479,760	4,860,541	4,878,836
CSS
Disaggregation of Revenue [Line Items]
Net sales										3,323,264	909,496	857,481
UBS
Disaggregation of Revenue [Line Items]
Net sales										3,522,971	2,588,880	2,440,284
UNITED STATES
Disaggregation of Revenue [Line Items]
Net sales										9,110,453	6,234,119	6,089,130
Canada
Disaggregation of Revenue [Line Items]
Net sales										1,892,321	1,647,066	1,647,933
Other International
Disaggregation of Revenue [Line Items]
Net sales	[1]									1,323,221	477,732	439,538
Shipping and Handling [Member]
Disaggregation of Revenue [Line Items]
Selling, general and administrative expense										$ 149,300	$ 71,700	$ 74,100
[1]	No individual other international country's net sales are material.

REVENUE Variable Consideration

REVENUE Variable Consideration (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue, Information Used to Assess Variable Consideration Constraint	269.5 million	106.6 million	107.4 million
Contract with Customer, Refund Liability	$ 38.9	$ 4.4

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative, Notional Amount	$ 111.9
Senior Notes [Member]
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Long-term debt	3,730.1	$ 850
Long-term Debt, Fair Value	$ 4,084.7	$ 866.2

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - TEXTUALS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-Lived Intangible Assets, Amortization Expense	$ 66,500	$ 35,500	$ 35,900
Goodwill [Line Items]
Disposal Group, Intangible Assets	5,722
Trademarks
Goodwill [Line Items]
Disposal Group, Intangible Assets	1,000
Customer Relationships
Goodwill [Line Items]
Disposal Group, Intangible Assets	3,300
Distribution agreements
Goodwill [Line Items]
Disposal Group, Intangible Assets	$ 1,400
EES
Goodwill [Line Items]
Goodwill, Gross				$ 809,900
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				10.00%

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF GOODWILL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Beginning balance January 1	$ 1,759,040	$ 1,722,603
Ending balance December 31	3,187,169	1,759,040
Goodwill, Acquired During Period	1,384,027	5,767
Goodwill, Foreign Currency Translation Gain (Loss)	44,102	30,670
Disposal Group, Including Discontinued Operation, Goodwill, Current	26,100
EES
Goodwill [Roll Forward]
Beginning balance January 1	573,447	542,704
Ending balance December 31	853,456	573,447
Goodwill, Acquired During Period	264,538	5,767
Goodwill, Foreign Currency Translation Gain (Loss)	15,471	24,976
Goodwill, Period Increase (Decrease)	20,200
UBS
Goodwill [Roll Forward]
Beginning balance January 1	949,882	945,450
Ending balance December 31	1,218,213	949,882
Goodwill, Acquired During Period	250,553	0
Goodwill, Foreign Currency Translation Gain (Loss)	17,778	4,432
Goodwill, Period Increase (Decrease)	11,700
CSS
Goodwill [Roll Forward]
Beginning balance January 1	235,711	234,449
Ending balance December 31	1,115,500	235,711
Goodwill, Acquired During Period	868,936	0
Goodwill, Foreign Currency Translation Gain (Loss)	10,853	$ 1,262
Goodwill, Period Increase (Decrease)	$ 2,000

GOODWILL AND INTANGIBLE ASSET_4

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF INTANGIBLE ASSETS BY MAJOR CLASS (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization		$ (261,424)	$ (280,442)
Intangible Assets Gross Excluding Goodwill		2,326,919	567,717
Intangible Assets, Net (Excluding Goodwill)		2,065,495	287,275
Trademarks
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	24,898	24,800
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(11,415)	(9,319)
Finite-Lived Intangible Assets, Net	[1]	13,483	15,481
Customer relationships
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	1,434,554	358,341
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(227,585)	(201,962)
Finite-Lived Intangible Assets, Net	[1]	1,206,969	156,379
Distribution agreements
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	29,212	37,371
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(21,040)	(25,294)
Finite-Lived Intangible Assets, Net	[1]	8,172	12,077
Non-compete agreements
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		4,462	196
Finite-Lived Intangible Assets, Accumulated Amortization		(1,384)	(180)
Finite-Lived Intangible Assets, Net		3,078	16
Patents
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		0	48,310
Finite-Lived Intangible Assets, Accumulated Amortization		0	(43,687)
Finite-Lived Intangible Assets, Net		$ 0	4,623
Finite-Lived Intangible Assets, Useful Life, Minimum		10 years
Trademarks
Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Gross		$ 833,793	$ 98,699
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
Minimum | Non-compete agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		2 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
Maximum | Non-compete agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		5 years
[1]	The net carrying amount as of December 31, 2020 excludes $1.0 million of trademarks, $3.3 million of customer relationships and $1.4 million of distribution agreements that are classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF EXPECTED AMORTIZATION EXPENSE (Details) $ in Thousands	Dec. 31, 2020USD ($)
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2021	$ 86,619
2022	83,628
2023	81,400
2024	80,087
2025	76,829
Thereafter	$ 823,139

ACQUISITIONS (Details)

ACQUISITIONS (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2020USD ($)countries$ / sharesshares	Dec. 31, 2020USD ($)countriesnumberOfCities$ / sharesshares	Dec. 31, 2019USD ($)shares	Jun. 22, 2020USD ($)$ / sharesshares	Dec. 31, 2018shares	Dec. 31, 2017shares
Business Acquisition [Line Items]
Goodwill, Acquired During Period		$ 1,384,027,000	$ 5,767,000
Preferred stock, shares issued | shares	21,612	21,612	0		0	0
Preferred stock, par value | $ / shares	$ 0.01	$ 0.01
Business Acquisition, Description of Acquired Entity		Anixter is a leading distributor of network and security solutions, electrical and electronic solutions, and utility power solutions with locations in over 300 cities across approximately 50 countries, and 2019 annual sales of more than $8 billion.
Business Combination, Reason for Business Combination		The Merger brought together two companies with highly compatible capabilities and characteristics. The combination of WESCO and Anixter created an enterprise with scale and should afford the Company the opportunity to digitize its business, and expand its services portfolio and supply chain offerings.
Number of Cities in which an Entity Operates | numberOfCities		300
Business Combination, Provisional Information, Initial Accounting Incomplete, Reasons		The estimated fair values of assets acquired and liabilities assumed are based on preliminary calculations and valuations using estimates and assumptions at the time of acquisition. The determination of the fair values of assets acquired and liabilities assumed, especially those related to identifiable intangible assets, is preliminary due to the complexity of combining multibillion dollar businesses. Accordingly, as the Company obtains additional information during the measurement period (not to exceed one year from the acquisition date), estimates and assumptions for the preliminary purchase consideration allocations may change materially.
Anixter International [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Jun. 22, 2020
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period		$ 8,000,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill				$ 1,838,065,000
Payments to Acquire Businesses, Gross		$ 3,811,038,000
Common stock, shares issued | shares				0.2397
Preferred stock, shares issued | shares				0.6356
Common Stock				$ 0.01
Preferred Stock, Dividend Rate, Percentage		10.625%
Preferred stock, par value | $ / shares				$ 25,000
Additional countries (in countries) | countries	50	50
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual		$ 4,500,000,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual		180,000,000
Business Acquisition, Transaction Costs	$ 132,200,000	132,200,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory		8,200,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Operating Lease Assets		18,000,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles	$ 6,400,000	5,400,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Noncurrent Assets		15,500,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Operating Lease Liabilities		17,000,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Income Taxes		27,500,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Noncurrent Liabilities		38,700,000
Goodwill, Purchase Accounting Adjustments		2,400,000
Business Acquisition, Pro Forma Revenue		$ 16,016,902,000	$ 17,204,472,000
Anixter International [Member] | Cash [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price | $ / shares				$ 72.82
Sylvania Lighting Services Corp. [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Mar. 5, 2019
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period		$ 100,000,000
Noncompete Agreements [Member] | Anixter International [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		2 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
Maximum [Member] | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		5 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
Minimum | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		2 years

SCHEDULE OF CONSIDERATION TRANS

SCHEDULE OF CONSIDERATION TRANSFERRED (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 3,707,575	$ 27,597	$ 0
Anixter International [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	3,811,038
Payment to Acquire Business, Fair Value of Cash Consideration	2,563,385
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	887,298
Payment for Debt Extinguishment or Debt Prepayment Cost	1,247,653
Business Combination, Consideration Transferred	4,698,336
Cash Acquired from Acquisition	103,463
Payments to Acquire Businesses, Net of Cash Acquired	3,707,575
Anixter International [Member] | Common Stock
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	2,476,010
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	313,512
Anixter International [Member] | Restricted Stock
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	87,375
Anixter International [Member] | Preferred Stock
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 573,786

SCHEDULE OF ASSUMED ASSETS AND

SCHEDULE OF ASSUMED ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jun. 22, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill	$ 3,187,169		$ 1,759,040	$ 1,722,603
Anixter International [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 103,463
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		1,306,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		116,386
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory		1,416,582
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets		54,978
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		211,721
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Assets		280,285
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		1,838,065
Goodwill		1,370,396
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets		139,760
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		6,838,536
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		920,163
Business Combination, Recongized Identifiable Assets Acquired and Liabilities Assumed, Accrued Payroll and Benefit Costs		69,480
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt		13,225
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other		222,119
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		77,617
Business Combination, Recognized Identifiable Asset Acquired and Liability Assumed, Lease Obligation		217,303
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities		374,734
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other		245,559
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		2,140,200
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net		$ 4,698,336

ANIXTER IDENTIFIABLE INTANGIBLE

ANIXTER IDENTIFIABLE INTANGIBLES (Details) - Anixter International [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Jun. 22, 2020
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			$ 1,838,065
Trademarks
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets			735,000
Customer-Related Intangible Assets
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			1,098,900
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	[1]	19 years
Noncompete Agreements [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			$ 4,165
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		2 years
[1]	Measurement period adjustments include an update to the estimated useful lives initially assigned to customer relationships, which resulted in income of $6.4 million during the year ended December 31, 2020.

ACQUISITIONS - BUSINESS ACQUISI

ACQUISITIONS - BUSINESS ACQUISITION, PRO FORMA INFORMATION (Details) - Anixter International [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	$ 16,016,902	$ 17,204,472
Business Acquisition, Pro Forma Net Income (Loss)	119,839	$ 285,100
Revenue
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Revenue	7,000
Net Income
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)	$ 201,300

ACQUISITIONS - SYLVANIA (Detail

ACQUISITIONS - SYLVANIA (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)numberOfEmployees	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Business Combinations [Abstract]
Payments to Acquire Businesses, Net of Cash Acquired	$ 3,707,575	$ 27,597	$ 0
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	3,707,575	$ 27,597	$ 0
Sylvania Lighting Services Corp. [Member]
Business Combinations [Abstract]
Business Acquisition, Goodwill, Expected Tax Deductible Amount	11,600
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	34,812
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	7,070
Payments to Acquire Businesses, Net of Cash Acquired	27,742
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	34,812
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	7,070
Payments to Acquire Businesses, Net of Cash Acquired	27,742
Business Acquisition, Goodwill, Expected Tax Deductible Amount	$ 11,600
Number of Employees Employed by the Entity | numberOfEmployees	220

ASSET AND LIABILITIES HELD FOR

ASSET AND LIABILITIES HELD FOR SALE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Revenue	$ 120,000
Disposal Group, Accounts, Notes and Loans Receivable, Net		$ 4,258
Disposal Group, Inventory		16,438
Disposal Group, Prepaid and Other Assets		395
Disposal Group, Property, Plant and Equipment		263
Disposal Group, Operating Lease Assets		1,938
Disposal Group, Intangible Assets		5,722
Disposal Group, Goodwill		26,059
Disposal Group, Assets		55,073
Disposal Group, Accounts Payable		3,639
Disposal Group, Other Liabilities, Current		541
Disposal Group, Operating Lease Liabilities		1,537
Disposal Group, Liabilities		$ 5,717

PROPERTY, BUILDINGS AND EQUIP_3

PROPERTY, BUILDINGS AND EQUIPMENT - SCHEDULE OF PROPERTY, BUILDINGS AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2020	[1]	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (312,106)		$ (268,415)
Property, buildings and equipment, net	399,157		181,448
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	169,873		110,056
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	266,317		162,029
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	235,666		127,919
Depreciable [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	671,856		400,004
Property, buildings and equipment, net	359,750		131,589
Land
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	26,409		24,106
Construction in progress
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	$ 12,998		$ 25,753
[1]	The components of property, buildings and equipment as of December 31, 2020 exclude a total of $0.3 million that is classified as held for sale, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

PROPERTY, BUILDINGS AND EQUIP_4

PROPERTY, BUILDINGS AND EQUIPMENT - PROPERTY, BUILDINGS AND EQUIPMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 40.8	$ 15.9	$ 17.3
Capitalized software amortization	14.3	10.6	$ 9.8
Unamortized software cost	123.9	29.8
Capitalized leases	25.7	6.5
Accumulated amortization related to capitalized leases	$ 7.9	$ 5.1

LEASES (Details)

LEASES (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	6 years 1 month 6 days	5 years 3 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent	4.60%	4.60%
Option to Extend Lessee's Operating Lease, Lease Payments	$ 17.4
Lessee, Operating Lease, Lease Not yet Commenced, Payments	$ 2.6
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	10 years

LEASES Supplemental balance she

LEASES Supplemental balance sheet information (Details) - USD ($) $ in Thousands		Dec. 31, 2020		Dec. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset		$ 534,705	[1]	$ 235,834	$ 240,000
Operating Lease, Liability, Noncurrent		414,889	[1]	179,830
Operating Lease, Liability		543,211	[1]	241,876	$ 245,000
Disposal Group, Operating Lease Assets		1,938
Disposal Group, Including Discontinued Operation, ST and LT Operating Lease Liabilities				2,100
Other Current Liabilities
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Current	[2]	$ 128,322	[1]	$ 62,046
[1]	Operating lease assets and liabilities of $1.9 million and $2.1 million, respectively, are classified as held for sale as of December 31, 2020, as disclosed in Note 7, "Assets and Liabilities Held for Sale".
[2]	Current operating lease liabilities are recorded as a component of other current liabilities in the Consolidated Balance Sheets.

LEASES Lease, Cost (Details)

LEASES Lease, Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 127,725	$ 73,613
Short-term Lease, Cost	494	90
Variable Lease, Cost	36,230	23,385
Lease, Cost	$ 164,449	$ 97,088

LEASES Supplemental Cash Flow I

LEASES Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Payments	$ 117,106	$ 75,775
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 121,207	$ 60,586

LEASES Lessee, Operating Lease,

LEASES Lessee, Operating Lease, Liability, Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2020		Dec. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 155,071
Lessee, Operating Lease, Liability, Payments, Due Year Two	127,851
Lessee, Operating Lease, Liability, Payments, Due Year Three	100,746
Lessee, Operating Lease, Liability, Payments, Due Year Four	72,847
Lessee, Operating Lease, Liability, Payments, Due Year Five	46,730
Lessee, Operating Lease, Liability, Payments, Due after Year Five	124,127
Lessee, Operating Lease, Liability, Payments, Due	627,372
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(84,161)
Operating Lease, Liability	$ 543,211	[1]	$ 241,876	$ 245,000
[1]	Operating lease assets and liabilities of $1.9 million and $2.1 million, respectively, are classified as held for sale as of December 31, 2020, as disclosed in Note 7, "Assets and Liabilities Held for Sale".

DEBT - SCHEDULE OF DEBT (Detail

DEBT - SCHEDULE OF DEBT (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount	$ 9,332
Finance Lease, Liability	17,931	$ 1,373
Total debt	4,975,983	1,292,628
Debt Instrument, Unamortized Premium	1,650	0
Debt Issuance Costs, Net	(78,850)	(8,876)
Less current and short-term portion	(528,830)	(26,685)
Total Long-term Debt, Excluding Current Maturities	4,369,953	1,257,067
Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Long-term debt	29,575	26,255
Accounts receivable securitization facility
Debt Instrument [Line Items]
Long-term debt	950,000	415,000
Revolving credit facility
Debt Instrument [Line Items]
Long-term debt	250,000	0
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	500,000	500,000
Senior Notes Due 2023
Debt Instrument [Line Items]
Long-term debt	58,636	0
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	350,000	350,000
Senior Notes Due 2025
Debt Instrument [Line Items]
Long-term debt	4,173	0
A7125 Senior Notes Due 2025
Debt Instrument [Line Items]
Long-term debt	1,500,000	0
A7250 Senior Notes Due 2028
Debt Instrument [Line Items]
Long-term debt	1,315,668	$ 0
Debt Instrument, Unamortized Discount	$ 9,332

DEBT (Details)

DEBT (Details) - USD ($)	Sep. 30, 2024	Jun. 14, 2022	Jun. 14, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 14, 2020
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				$ 950,000,000	$ 415,000,000
Percentage of principal amount of Senior Notes accelerated under default				0.25
Debt Issuance Costs, Net				$ (78,850,000)	$ (8,876,000)
Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate				3.40%	6.32%
Long-term debt				$ 29,575,000	$ 26,255,000
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date				Jun. 22, 2023
Debt Instrument, Fee				0.45
Accounts Receivable Eligible for Securitization				$ 1,476,100,000	809,500,000
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate				1.60%
Long-term debt				$ 950,000,000	415,000,000
Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Opportunity to Increase Borrowing Capacity				500,000,000
Debt Instrument, Unused Borrowing Capacity, Amount				$ 1,100,000,000		$ 1,200,000,000
Debt Instrument, Interest Rate During Period				1.60%
Debt Instrument, Increase, Additional Borrowings				$ 1,197,900,000	715,400,000
Debt Instrument, Decrease, Repayments				948,000,000	767,400,000
Long-term debt				250,000,000	0
Line of Credit Facility, Remaining Borrowing Capacity				801,500,000	563,800,000
Revolving credit facility | Letter of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount				$ 175,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date				Dec. 15, 2021
Long-term debt				$ 3,730,100,000	850,000,000
Debt Instrument, Interest Rate, Stated Percentage				5.375%
Debt Instrument, Face Amount				$ 500,000,000
Deferred Finance Costs, Gross				$ 8,400,000
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date				Jun. 15, 2024
Long-term debt				$ 350,000,000	350,000,000
Debt Instrument, Interest Rate, Stated Percentage				5.375%
Debt Instrument, Face Amount				$ 350,000,000
Deferred Finance Costs, Gross				$ 6,000,000
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed				101.00%
5.50% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt				$ 58,600,000
Debt Instrument, Interest Rate, Stated Percentage				5.50%
Debt Instrument, Face Amount				$ 350,000,000
Senior Notes tender offer consideration per $1,000 principal amount				50
6.00% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt				$ 4,200,000
Debt Instrument, Interest Rate, Stated Percentage				6.00%
Debt Instrument, Face Amount				$ 250,000,000
Senior Notes consent fee per $1,000 principal amount				2.50
Senior Notes tender offer consideration per $1,000 principal amount				$ 1,012.50
A7125 Senior Notes Due 2025
Debt Instrument [Line Items]
Debt Instrument, Maturity Date				Jun. 15, 2025
Debt Instrument, Issuance Date				Jun. 12, 2020
Long-term debt				$ 1,500,000,000	0
Debt Instrument, Interest Rate, Stated Percentage				7.125%
Debt Instrument, Face Amount				$ 1,500,000,000
Discount percentage of par value				100.00%
Deferred Finance Costs, Gross				$ 33,100,000
Debt Instrument, Redemption Price, Percentage				35.00%
A7250 Senior Notes Due 2028
Debt Instrument [Line Items]
Debt Instrument, Maturity Date				Jun. 15, 2028
Debt Instrument, Issuance Date				Jun. 12, 2020
Long-term debt				$ 1,315,668,000	0
Debt Instrument, Interest Rate, Stated Percentage				7.25%
Debt Instrument, Face Amount				$ 1,325,000,000
Discount percentage of par value				99.244%
Deferred Finance Costs, Gross				$ 29,300,000
Debt Instrument, Redemption Price, Percentage				35.00%
Minimum | Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 2,000,000
Minimum | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 600,000,000
Debt Instrument, Basis Spread on Variable Rate				0.95%
Maximum | Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 31,000,000
Maximum | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 1,025,000,000		$ 1,200,000,000
Debt Instrument, Basis Spread on Variable Rate				1.20%
Accordion Feature [Member] | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount				$ 375,000,000
Standby Letters of Credit [Member] | Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity				$ 28,400,000	48,500,000
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 due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	100.00%	101.344%	102.688%
Surety Bond [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					36,100,000
Property Lease Guarantee [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity					$ 7,800,000

DEBT - SCHEDULE OF MATURITIES O

DEBT - SCHEDULE OF MATURITIES OF LONG-TERM DEBT (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
2021	$ 529,869
2022	4,051
2023	1,016,322
2024	352,183
2025	1,756,055
Thereafter	1,326,835
Total payments on debt	4,985,315
Debt discount on convertible debentures	(9,332)
Debt and Lease Obligation	$ 4,975,983	$ 1,292,628

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Preferred stock, shares issued	21,612	0	0	0
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
Series A Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	25,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01
Preferred Stock, Dividend Payment Rate, Variable	10.325
Preferred Stock, Liquidation Preference Per Share	$ 25,000
Preferred Stock, Dividend Rate, Percentage	10.625%
Preferred stock, shares issued	21,612
Depositary Share [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	21,611,534

INCOME TAXES - ADDITIONAL INFOR

INCOME TAXES - ADDITIONAL INFORMATION (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Deferred Income Tax Expense (Benefit)			$ 900
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount		$ 3,700	3,400
Amortization of intangible assets	$ 540,520	159,573
Deferred Tax Assets, Tax Deferred Expense, Other	8,200
Deferred Tax Assets, Operating Loss Carryforwards	36,923	10,486
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	55,637	1,247
Deferred Tax Assets, Valuation Allowance	60,629	5,854
Unrecognized Tax Benefits	68,075	54	1,293	$ 4,348
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	29,100	100	1,300
Decrease in Unrecognized Tax Benefits is Reasonably Possible	3,600
Interest related to uncertain tax positions	300	800	$ 200
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	5,500	100
Undistributed Earnings of Foreign Subsidiaries	1,835,000
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries	75,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued	1,500
General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Valuation Allowance	30,100	1,200
Anixter International [Member]
Operating Loss Carryforwards [Line Items]
Amortization of intangible assets	347,300
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Taxes Payable	63,300	36,800
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	34,500	7,900
Operating Loss Carryforwards, Valuation Allowance	22,300	4,600
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	55,600	1,200
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	2,400	$ 2,600
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 4,200

INCOME TAXES - SCHEDULE OF INCO

INCOME TAXES - SCHEDULE OF INCOME BEFORE INCOME TAX, DOMESTIC AND FOREIGN (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
United States									$ 26,031	$ 198,566	$ 198,556
Foreign									96,811	83,495	82,469
Income before income taxes	$ 19,384	$ 104,332	$ (45,313)	$ 44,441	$ 67,587	$ 80,225	$ 80,643	$ 53,606	$ 122,842	$ 282,061	$ 281,025

INCOME TAXES - SCHEDULE OF COMP

INCOME TAXES - SCHEDULE OF COMPONENTS OF INCOME TAX EXPENSE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current taxes
Federal	$ 25,605	$ 31,695	$ 28,464
State	11,322	8,616	7,458
Foreign	19,414	6,347	10,611
Total current	56,341	46,658	46,533
Deferred taxes
Federal	(17,913)	6,774	5,253
State	(7,264)	1,846	1,967
Foreign	(8,361)	4,585	1,917
Total deferred	(33,538)	13,205	9,137
Income tax expense	$ 22,803	$ 59,863	$ 55,670

INCOME TAXES - SCHEDULE OF EFFE

INCOME TAXES - SCHEDULE OF EFFECTIVE INCOME TAX RATE RECONCILIATION (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	21.00%	21.00%
State taxes, net of federal tax benefit	(1.40%)	(3.10%)	2.80%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	0.00%	(1.30%)	(1.20%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	0.00%	0.00%	(0.30%)
Effective Income Tax Rate Reconciliation, Deduction, Percent	(13.40%)	(5.50%)	(5.60%)
Unrecognized tax benefits	2.10%	0.40%	0.10%
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent	5.70%	0.70%	1.00%
Foreign Income Tax Expense (Benefit), Continuing Operations	1.80%	0.60%	0.60%
Other	0.00%	3.00%	1.60%
Effective income tax rate	18.60%	21.20%	19.80%

INCOME TAXES - SCHEDULE OF DEFE

INCOME TAXES - SCHEDULE OF DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets, Net [Abstract]
Accounts receivable	$ 17,560	$ 3,382
Deferred Tax Assets, Inventory	14,793
Deferred Tax Assets, Property, Plant and Equipment	134,377	61,326
Employee benefits	53,040	20,641
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	14,061	13,792
Tax loss carryforwards	36,923	10,486
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	55,637	1,247
Other	27,643	6,791
Deferred taxes, Assets	293,405	111,811
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Inventory		4,580
Depreciation	60,687	18,393
Deferred Tax Liabilities, Leasing Arrangements	136,477	60,670
Amortization of intangible assets	540,520	159,573
Other	6,286	3,964
Deferred Tax Assets, Gross	354,034	117,665
Deferred Tax Assets, Valuation Allowance	(60,629)	(5,854)
Deferred Tax Liabilities, Gross	743,970	$ 247,180
Anixter International [Member]
Deferred Tax Liabilities [Abstract]
Amortization of intangible assets	$ 347,300

INCOME TAXES - SCHEDULE OF IN_2

INCOME TAXES - SCHEDULE OF INCOME TAX CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance January 1	$ 54	$ 1,293	$ 4,348
Additions based on tax positions related to the current year	14,009	0	0
Unrecognized Tax Benefits, Increase Resulting from Acquisition	68,048	0	0
Reductions for tax positions of prior years	(43)	0	0
Settlements	0	(1,290)	(2,646)
Lapse in statute of limitations	(15,886)	0	(287)
Unrecognized Tax Benefits, Increase Resulting from Foreign Currency Translation	1,893	51
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation			(122)
Ending balance December 31	$ 68,075	$ 54	$ 1,293

EARNINGS PER SHARE - SCHEDULE O

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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock									$ 2,901	$ 153,049	$ 127,169
Stock Repurchase Program, Authorized Amount	$ 400,000				$ 300,000				$ 400,000	$ 300,000	$ 300,000
Stock Repurchase Program Expiration Date									Dec. 31, 2020
Treasury Stock, Shares, Acquired										3,455,584	2,003,446
Preferred Stock Dividends, Income Statement Impact									$ 30,139	$ 0	$ 0
Weighted average common shares outstanding used in computing basic earnings per share									46,174,000	43,104,000	46,722,000
Common shares issuable upon exercise of dilutive stock options									451,000	383,000	477,000
Weighted average common shares outstanding and common share equivalents used in computing diluted earnings per share									46,625,000	43,487,000	47,199,000
Earnings Per Share attributable to WESCO International, Inc.
Basic	$ 0.11	$ 1.32	$ (0.84)	$ 0.82	$ 1.27	$ 1.53	$ 1.46	$ 0.94	$ 1.53	$ 5.18	$ 4.87
Diluted	$ 0.11	$ 1.31	$ (0.84)	$ 0.82	$ 1.26	$ 1.52	$ 1.45	$ 0.93	$ 1.51	$ 5.14	$ 4.82
Net Income (Loss) Available to Common Stockholders, Basic	$ 5,632	$ 66,167	$ (35,782)	$ 34,407	$ 53,098	$ 64,495	$ 63,464	$ 42,369	$ 70,421	$ 223,426	$ 227,343
Net Income attributable to WESCO International, Inc.									100,560	223,426	$ 227,343
Treasury Stock, Common [Member]
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock			$ 150,000						$ 275,000	$ 125,000
Treasury Stock, Common, Shares	5,459,030			365,272					5,459,030
Treasury Stock, Shares, Acquired									3,090,312	2,368,738

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Payments for Repurchase of Common Stock		$ 2,901	$ 153,049	$ 127,169
Treasury Stock, Shares, Acquired			3,455,584	2,003,446
Stock Appreciation Rights (SARs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share		1,800,000	1,700,000	1,600,000
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
Treasury Stock, Shares, Acquired		3,090,312	2,368,738

Textuals (Details)

Textuals (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)numberOfPlans	Dec. 31, 2019USD ($)		Dec. 31, 2018USD ($)
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer discretionary contribution amount				$ 20,600
Defined contribution plan, cost recognized	$ 18,300	$ 22,900		42,900
Assets Held-in-trust	$ 39,600
Defined Benefit Plan, Description	WESCO sponsors a contributory defined benefit plan (the "EECOL Plan") covering substantially all Canadian employees of EECOL. The EECOL Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the EECOL 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	WESCO also sponsors a Supplemental Executive Retirement Plan (the "EECOL SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the EECOL SERP was closed to new participants and existing participants became 100% vested. EECOL SERP participants continue to contribute 4% of their earnings to the EECOL Plan.
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.20%	3.20%	[1]
Defined Benefit Plan, Benefit Obligation	$ 819,339	$ 134,852	[1]	105,515	[1]
DefinedBenefitPlanNumberOfPlansWithProjectedBenefitObligationsInExcessOfFairValueOfPlanAssets | numberOfPlans	13
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	$ 504,800
Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets	365,400
Defined Benefit Plan, Plan Assets, Amount	$ 721,005	103,385	[1]	86,556	[1]
Accumulated Benefit Obligation (ABO) at December 31		104,600
DefinedBenefitPlanNumberOfPlansWithAccumulatedBenefitObligationsInExcessOfFairValueOfPlanAssets | numberOfPlans	13
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation	$ 435,600
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets	365,400
Service Cost	$ 10,792	4,602	[1]	5,242
Defined Benefit Plan Assets Actual Gain Loss	13.60%
Defined Benefit Plan, Expected Future Benefit Payment, Year One	$ 38,400
WESCO [Member]
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%
Anixter Employee Savings Plan [Member]
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	5.00%
WESCO Deferred Compensation Plan
Schedule of Employee Benefit Plans [Line Items]
Deferred Compensation Liability, Current	$ 10,100
Deferred Compensation Liability, Classified, Noncurrent	17,300	$ 25,200
AnixterDeferred Compensation Plan
Schedule of Employee Benefit Plans [Line Items]
Deferred Compensation Liability, Current	$ 45,100
Foreign Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.00%	3.20%	[1]
Defined Benefit Plan, Benefit Obligation	$ 486,855	$ 134,852	[1]	105,515	[1]
Defined Benefit Plan, Plan Assets, Amount	365,718	103,385	[1]	86,556	[1]
Accumulated Benefit Obligation (ABO) at December 31	417,600
Service Cost	9,029	$ 4,602	[1]	5,242
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	11,400
Defined Benefit Plan, Expected Future Benefit Payment, Year One	$ 9,873
United States
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.60%	0.00%
Defined Benefit Plan, Benefit Obligation	$ 332,484	$ 0		0
Defined Benefit Plan, Plan Assets, Amount	355,287	0		0
Accumulated Benefit Obligation (ABO) at December 31	328,200
Service Cost	1,763	0		0
Defined Benefit Plan, Expected Future Benefit Payment, Year One	$ 28,527
Minimum | WESCO Distribution Canada Defined Contribution plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	3.00%
Minimum | Anixter Employee Savings Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined contribution discretionary contribution percentage	2.00%
Maximum | WESCO Distribution Canada Defined Contribution plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	5.00%
Maximum | Anixter Employee Savings Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined contribution discretionary contribution percentage	2.50%
Pension Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Other Nonoperating Gains (Losses)	$ (8,200)	$ (1,400)		$ (1,900)
Pension Plan [Member] | Foreign Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Benefit Obligation	486,800
Pension Plan [Member] | United States
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Year One	18,100
WESCO Deferred Compensation Plan
Schedule of Employee Benefit Plans [Line Items]
Deferred Compensation Liability, Current and Noncurrent	$ 27,400
[1]	For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP

EMPLOYEE BENEFIT PLANS Benefit

EMPLOYEE BENEFIT PLANS Benefit Obligations, Plan Assets, and Funded Status (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan Disclosure
Defined Benefit Plan, Benefit Obligation		$ 819,339	$ 134,852	[1]	$ 105,515	[1]
Defined Benefit Plan, Benefit Obligation, Business Combination	[2]	619,099	0	[1]
Service Cost		10,792	4,602	[1]	5,242
Interest cost		11,949	4,362	[1]	4,137
Participant contributions		728	736	[1]
Actuarial (gain) loss		26,955	18,591	[1]
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(13,230)	(4,459)	[1]
DefinedBenefitPlanBenefitsPaidFromCompanyAssets		(995)	0	[1]
Curtailment		(101)	0	[1]
Plan Amendment		(37)	0	[1]
Settlement		(1,235)	0	[1]
Foreign Currency Translation Gain (Loss)		30,562	5,505	[1]
Defined Benefit Plan, Plan Assets, Amount		721,005	103,385	[1]	86,556	[1]
Defined Benefit Plan, Plan Assets, Business Combination	[2]	542,936	0	[1]
Actual return on plan assets		59,164	12,763	[1]
Participant contributi		728	736	[1]
Company contributions		6,838	3,198	[1]
Defined Benefit Plan, Plan Assets, Benefits Paid		(13,230)	(4,459)	[1]
Settlement		(1,235)	0	[1]
Foreign Currency Translation Gain (Loss)		22,419	4,591	[1]
Funded status		(98,334)	(31,467)	[1]
Assets for Plan Benefits, Defined Benefit Plan		41,100	0	[1]
Current liabilities		(18,589)	(383)	[1]
Non-current liabilities		$ (120,845)	$ (31,084)	[1]
Discount rate		2.20%	3.20%	[1]
Average salary increases		3.40%	3.50%	[1]
United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Benefit Obligation		$ 332,484	$ 0		0
Defined Benefit Plan, Benefit Obligation, Business Combination	[2]	317,893	0
Service Cost		1,763	0		0
Interest cost		4,787	0		0
Participant contributions		0	0
Actuarial (gain) loss		12,911	0
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(4,222)	0
DefinedBenefitPlanBenefitsPaidFromCompanyAssets		(547)	0
Curtailment		(101)	0
Plan Amendment		0	0
Settlement		0	0
Foreign Currency Translation Gain (Loss)		0	0
Defined Benefit Plan, Plan Assets, Amount		355,287	0		0
Defined Benefit Plan, Plan Assets, Business Combination	[2]	324,292	0
Actual return on plan assets		35,217	0
Participant contributi		0	0
Company contributions		0	0
Defined Benefit Plan, Plan Assets, Benefits Paid		(4,222)	0
Settlement		0	0
Foreign Currency Translation Gain (Loss)		0	0
Funded status		22,803	0
Assets for Plan Benefits, Defined Benefit Plan		40,921	0
Current liabilities		(18,118)	0
Non-current liabilities		$ 0	$ 0
Discount rate		2.60%	0.00%
Average salary increases		3.80%	0.00%
Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Benefit Obligation		$ 486,855	$ 134,852	[1]	105,515	[1]
Defined Benefit Plan, Benefit Obligation, Business Combination	[2]	301,206	0	[1]
Service Cost		9,029	4,602	[1]	5,242
Interest cost		7,162	4,362	[1]	4,137
Participant contributions		728	736	[1]
Actuarial (gain) loss		14,044	18,591	[1]
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(9,008)	(4,459)	[1]
DefinedBenefitPlanBenefitsPaidFromCompanyAssets		(448)	0	[1]
Curtailment		0	0	[1]
Plan Amendment		(37)	0	[1]
Settlement		(1,235)	0	[1]
Foreign Currency Translation Gain (Loss)		30,562	5,505	[1]
Defined Benefit Plan, Plan Assets, Amount		365,718	103,385	[1]	$ 86,556	[1]
Defined Benefit Plan, Plan Assets, Business Combination	[2]	218,644	0	[1]
Actual return on plan assets		23,947	12,763	[1]
Participant contributi		728	736	[1]
Company contributions		6,838	3,198	[1]
Defined Benefit Plan, Plan Assets, Benefits Paid		(9,008)	(4,459)	[1]
Settlement		(1,235)	0	[1]
Foreign Currency Translation Gain (Loss)		22,419	4,591	[1]
Funded status		(121,137)	(31,467)	[1]
Assets for Plan Benefits, Defined Benefit Plan		179	0	[1]
Current liabilities		(471)	(383)	[1]
Non-current liabilities		$ (120,845)	$ (31,084)	[1]
Discount rate		2.00%	3.20%	[1]
Average salary increases		3.20%	3.50%	[1]
[1]	For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP
[2]	As described above, the Company assumed the Domestic Plans and certain foreign plans in connection with the June 22, 2020 acquisition of Anixter.

EMPLOYEE BENEFIT PLANS Pension

EMPLOYEE BENEFIT PLANS Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan Disclosure
Service Cost	$ 10,792	$ 4,602	[1]	$ 5,242
Interest cost	11,949	4,362	[1]	4,137
Expected return on plan assets	(20,054)	(5,695)		(5,969)
Recognized actuarial gain	0	(63)		(46)
Settlement	(144)	0		0
Total net periodic pension (benefit) cost	2,543	3,206		3,364
United States
Defined Benefit Plan Disclosure
Service Cost	1,763	0		0
Interest cost	4,787	0		0
Expected return on plan assets	(8,395)	0		0
Recognized actuarial gain	0	0		0
Settlement	0	0		0
Total net periodic pension (benefit) cost	(1,845)	0		0
Foreign Plan [Member]
Defined Benefit Plan Disclosure
Service Cost	9,029	4,602	[1]	5,242
Interest cost	7,162	4,362	[1]	4,137
Expected return on plan assets	(11,659)	(5,695)		(5,969)
Recognized actuarial gain	0	(63)		(46)
Settlement	(144)	0		0
Total net periodic pension (benefit) cost	$ 4,388	$ 3,206		$ 3,364
[1]	For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP

EMPLOYEE BENEFIT PLANS Assumpti

EMPLOYEE BENEFIT PLANS Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate	2.50%	4.00%	3.50%
Expected Long-term Rate of Return on Plan Assets	5.30%	6.40%	6.40%
Rate of Compensation Increase	3.50%	3.80%	3.80%
Foreign Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate	2.20%	4.00%	3.50%
Expected Long-term Rate of Return on Plan Assets	5.20%	6.40%	6.40%
Rate of Compensation Increase	3.40%	3.80%	3.80%
United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount Rate	2.90%	0.00%	0.00%
Expected Long-term Rate of Return on Plan Assets	5.50%	0.00%	0.00%
Rate of Compensation Increase	3.80%	0.00%	0.00%

EMPLOYEE BENEFIT PLANS - AOCI (

EMPLOYEE BENEFIT PLANS - AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	$ (3,062)	$ 8,890	$ (2,696)
Prior Service Cost (Credit), before Tax	(37)	0
Actuarial (Gain) Loss Arising During Period, before Tax	(12,154)	11,586
Curtailment	(101)	0
Settlement	144	0
Foreign currency translation Gain Loss	196	0
Prior Service Cost (Credit), before Tax	(37)	0
Actuarial (Gain) Loss, before Tax	(3,025)	8,890
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	562	(2,329)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	$ (2,500)	$ 6,561

EMPLOYEE BENEFIT PLANS Benefi_2

EMPLOYEE BENEFIT PLANS Benefit payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payment, Year One	$ 38,400
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	21,143
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	22,678
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	24,191
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	25,795
Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years	161,300
United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payment, Year One	28,527
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	11,165
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	12,065
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	13,046
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	13,807
Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years	78,122
Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Expected Future Benefit Payment, Year One	9,873
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	9,978
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	10,613
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	11,145
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	11,988
Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years	$ 83,178

EMPLOYEE BENEFIT PLANS Asset al

EMPLOYEE BENEFIT PLANS Asset allocations (Details)	Dec. 31, 2020	Dec. 31, 2019
United States
Defined Benefit Plan Disclosure
Total investments	100.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	100.00%
Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	100.00%	100.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	100.00%	100.00%
Defined Benefit Plan, Equity Securities | United States
Defined Benefit Plan Disclosure
Total investments	38.60%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	37.00%
Defined Benefit Plan, Equity Securities | United States | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	30.00%
Defined Benefit Plan, Equity Securities | United States | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	45.00%
Defined Benefit Plan, Equity Securities | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	38.10%	40.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	41.00%	40.00%
Defined Benefit Plan, Equity Securities | Foreign Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	25.00%
Defined Benefit Plan, Equity Securities | Foreign Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	48.00%
US Treasury and Government | United States
Defined Benefit Plan Disclosure
Total investments	22.20%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	24.00%
US Treasury and Government | United States | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	0.00%
US Treasury and Government | United States | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	40.00%
Corporate Debt Securities | United States
Defined Benefit Plan Disclosure
Total investments	6.70%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	8.00%
Corporate Debt Securities | United States | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	0.00%
Corporate Debt Securities | United States | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	40.00%
Corporate Debt Securities | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	5.90%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	1.00%
Corporate Debt Securities | Foreign Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	1.00%
Corporate Debt Securities | Foreign Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	37.00%
Other Debt Obligations | United States
Defined Benefit Plan Disclosure
Total investments	15.60%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	14.00%
Other Debt Obligations | United States | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	9.00%
Other Debt Obligations | United States | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	19.00%
Other Debt Obligations | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	40.60%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	44.00%
Other Debt Obligations | Foreign Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	26.00%
Other Debt Obligations | Foreign Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	65.00%
Defined Benefit Plan, Debt Security | United States
Defined Benefit Plan Disclosure
Total investments	44.50%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	46.00%
Defined Benefit Plan, Debt Security | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	46.50%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	45.00%
Real Estate Funds | United States
Defined Benefit Plan Disclosure
Total investments	14.80%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	16.00%
Real Estate Funds | United States | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	9.00%
Real Estate Funds | United States | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	23.00%
Real Estate Funds | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	4.80%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	6.00%
Real Estate Funds | Foreign Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	2.00%
Real Estate Funds | Foreign Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	8.00%
Other Investments [Member]
Defined Benefit Plan Disclosure
Total investments		15.20%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities		15.00%
Other Investments [Member] | United States
Defined Benefit Plan Disclosure
Total investments	2.10%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	1.00%
Other Investments [Member] | United States | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	0.00%
Other Investments [Member] | United States | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	5.00%
Other Investments [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	5.20%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	3.00%
Other Investments [Member] | Foreign Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	3.00%
Other Investments [Member] | Foreign Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	12.00%
Insurance product | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments	5.40%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	5.00%
Insurance product | Foreign Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	5.00%
Insurance product | Foreign Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	5.00%
Equity Securities, Canadian | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		12.50%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities		12.50%
Defined Benefit Plan, Equity Securities, US | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		5.00%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities		5.00%
Defined Benefit Plan, Equity Securities, Non-US | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		22.50%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities		22.50%
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Total investments		44.80%
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities		45.00%

EMPLOYEE BENEFIT PLANS Fair val

EMPLOYEE BENEFIT PLANS Fair value plan assets (Details) - USD ($) $ in Thousands		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 721,005		$ 103,385	[1]	$ 86,556	[1]
Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		100.00%		100.00%
Defined Benefit Plan, Plan Assets, Amount		$ 365,718		$ 103,385	[1]	86,556	[1]
United States
Defined Benefit Plan Disclosure
Total investments		100.00%
Defined Benefit Plan, Plan Assets, Amount		$ 355,287		0		$ 0
Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		8,049
Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		747		224
Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		7,302
Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		19,611
Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		19,611		0
Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0		0
Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	693,345
Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		345,360	[2]	$ 103,161	[3]
Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	347,985
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Total investments				44.80%
Fixed Income Investments [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[3]			$ 46,309
Fixed Income Investments [Member] | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Fixed Income Investments [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Fixed Income Investments [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				$ 0
Other Investments [Member]
Defined Benefit Plan Disclosure
Total investments				15.20%
Defined Benefit Plan, Plan Assets, Amount		$ 26,361
Other Investments [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		5.20%
Defined Benefit Plan, Plan Assets, Amount		$ 19,059		$ 15,704
Other Investments [Member] | United States
Defined Benefit Plan Disclosure
Total investments		2.10%
Defined Benefit Plan, Plan Assets, Amount		$ 7,302
Other Investments [Member] | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		8,049
Other Investments [Member] | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		747		224
Other Investments [Member] | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		7,302
Other Investments [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Investments [Member] | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0		0
Other Investments [Member] | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Investments [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Investments [Member] | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0		0
Other Investments [Member] | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Investments [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	18,312
Other Investments [Member] | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		18,312	[2]	$ 15,480	[3]
Other Investments [Member] | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	0
Defined Benefit Plan, Equity Securities
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 276,635
Defined Benefit Plan, Equity Securities | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		38.10%		40.00%
Defined Benefit Plan, Plan Assets, Amount		$ 139,537
Defined Benefit Plan, Equity Securities | United States
Defined Benefit Plan Disclosure
Total investments		38.60%
Defined Benefit Plan, Plan Assets, Amount		$ 137,098
Defined Benefit Plan, Equity Securities | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Defined Benefit Plan, Equity Securities | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	276,635
Defined Benefit Plan, Equity Securities | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	139,537
Defined Benefit Plan, Equity Securities | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	137,098
US Treasury and Government
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		78,808
US Treasury and Government | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 0
US Treasury and Government | United States
Defined Benefit Plan Disclosure
Total investments		22.20%
Defined Benefit Plan, Plan Assets, Amount		$ 78,808
US Treasury and Government | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
US Treasury and Government | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	78,808
US Treasury and Government | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	0
US Treasury and Government | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	78,808
Corporate Debt Securities
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 45,501
Corporate Debt Securities | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		5.90%
Defined Benefit Plan, Plan Assets, Amount		$ 21,677
Corporate Debt Securities | United States
Defined Benefit Plan Disclosure
Total investments		6.70%
Defined Benefit Plan, Plan Assets, Amount		$ 23,824
Corporate Debt Securities | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Corporate Debt Securities | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	45,501
Corporate Debt Securities | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	21,677
Corporate Debt Securities | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	23,824
Other Debt Obligations
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 204,016
Other Debt Obligations | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		40.60%
Defined Benefit Plan, Plan Assets, Amount		$ 148,469
Other Debt Obligations | United States
Defined Benefit Plan Disclosure
Total investments		15.60%
Defined Benefit Plan, Plan Assets, Amount		$ 55,547
Other Debt Obligations | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Other Debt Obligations | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	204,016
Other Debt Obligations | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	148,469
Other Debt Obligations | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	55,547
Real Estate Funds
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 70,073
Real Estate Funds | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		4.80%
Defined Benefit Plan, Plan Assets, Amount		$ 17,365
Real Estate Funds | United States
Defined Benefit Plan Disclosure
Total investments		14.80%
Defined Benefit Plan, Plan Assets, Amount		$ 52,708
Real Estate Funds | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Real Estate Funds | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	70,073
Real Estate Funds | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	17,365
Real Estate Funds | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	52,708
Insurance product
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		$ 19,611
Insurance product | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments		5.40%
Defined Benefit Plan, Plan Assets, Amount		$ 19,611
Insurance product | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 1 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		19,611
Insurance product | Level 2 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		19,611
Insurance product | Level 2 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 3 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Level 3 | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount		0
Insurance product | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	0
Insurance product | Fair Value Measured at Net Asset Value Per Share | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	0
Insurance product | Fair Value Measured at Net Asset Value Per Share | United States
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	[2]	$ 0
Defined Benefit Plan, Equity Securities, US | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments				5.00%
Defined Benefit Plan, Plan Assets, Amount	[3]			$ 5,160
Defined Benefit Plan, Equity Securities, US | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Defined Benefit Plan, Equity Securities, US | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Defined Benefit Plan, Equity Securities, US | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				$ 0
Defined Benefit Plan, Equity Securities, Non-US | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments				22.50%
Defined Benefit Plan, Plan Assets, Amount	[3]			$ 23,239
Defined Benefit Plan, Equity Securities, Non-US | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Defined Benefit Plan, Equity Securities, Non-US | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Defined Benefit Plan, Equity Securities, Non-US | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				$ 0
Equity Securities, Canadian | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Total investments				12.50%
Defined Benefit Plan, Plan Assets, Amount	[3]			$ 12,973
Equity Securities, Canadian | Level 1 | Foreign Plan [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Equity Securities, Canadian | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				0
Equity Securities, Canadian | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount				$ 0
[1]	For 2019, the changes in benefit obligations, plan assets and funded status relate to the EECOL Plan and the EECOL SERP
[2]	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 table are intended to reconcile the fair value hierarchy to the total fair value of plan assets
[3]	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 table are intended to reconcile the fair value hierarchy to the total fair value of plan assets.

EMPLOYEE BENEFIT PLANS - Other

EMPLOYEE BENEFIT PLANS - Other Benefits (Details) - Phantom Share Units (PSUs) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Defined Benefit Plan Disclosure
Other Deferred Compensation Arrangements, Liability, Classified, Noncurrent	$ 22.8
Share-based Payment Arrangement, Expense	$ 9.2

STOCK-BASED COMPENSATION (Detai

STOCK-BASED COMPENSATION (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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				$ 19,279	$ 19,062	$ 16,445
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value				$ 8,800	10,700	8,200
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				1,100,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 33,500
Share-based Payment Arrangement, Expense, Tax Benefit				$ 2,000	$ 2,500	$ 2,000
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				$ 13.86	$ 16.36	$ 18.38
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				921,495	363,729	327,798	290,054
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 37.44	$ 54.13	$ 62.40
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 19,300	$ 19,100	$ 16,400
Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3,600	$ 12,300	$ 17,600
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				305,269

STOCK-BASED COMPENSATION - SCHE

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, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 47.11	$ 35.01	$ 40.74
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	305,269	195,305	138,896	148,508
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 49.56	$ 54.64	$ 62.80
Share Based Compensation Arrangements By Share Based Payment Award, Options and Stock Appreciation Rights Outstanding [Roll Forward]
Stock-settled appreciation rights granted	158,756	126,874	44,144
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	$ 13.86	$ 16.36	$ 18.38
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	391,339	113,099	192,700
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures	46,245	115,103	203,320
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 65.93	$ 65.27	$ 68.69
Weighted Average Remaining Contractual Term, Outstanding	5 years 8 months 12 days
Weighted Average Remaining Contractual Term, Exercisable	4 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding	$ 39,834
Aggregate Intrinsic Value, Exercisable	$ 26,622
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	1,630,891	1,723,370	1,453,932
Stock-settled appreciation rights granted	262,091	213,618	509,046
Share-based Payment Arrangement, Option, Exercise Price Range, Exercisable, Weighted Average Exercise Price	$ 62.72	$ 59	$ 57.93
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 60.48	$ 59.72	$ 59.26	$ 57.75
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	2,161,556	2,337,049	2,351,633	2,238,607
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 48.32	$ 54.63	$ 62.68
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	132,838
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	19,797

STOCK-BASED COMPENSATION - SUMM

STOCK-BASED COMPENSATION - SUMMARY OF RESTRICTED STOCK UNITS AND PERFORMANCE-BASED AWARDS (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	305,269	195,305	138,896	148,508
Granted	158,756	126,874	44,144
Vested in Period	(25,909)	(25,696)	0
Unvested, Weighted Average Fair Value	$ 52.61	$ 60.24	$ 59.33	$ 60.23
Granted, Weighted Average Fair Value	49.56	54.64	62.80
Vested in Period, Weighted Average Fair Value	$ 78.04	$ 42.44	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(22,883)	(44,769)	(53,756)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 69.39	$ 52.11	$ 64.67
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	921,495	363,729	327,798	290,054
Granted	656,717	192,106	122,062
Vested in Period	(83,253)	(136,777)	(64,166)
Unvested, Weighted Average Fair Value	$ 43.15	$ 60	$ 57.87	$ 58.11
Granted, Weighted Average Fair Value	37.44	54.13	62.40
Vested in Period, Weighted Average Fair Value	$ 69.17	$ 46.52	$ 67.91
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(15,698)	(19,398)	(20,152)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 56.79	$ 59.62	$ 58.15
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	305,269
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	132,838
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	19,797
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	152,634

STOCK-BASED COMPENSATION - SC_2

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED PAYMENT AWARDS, VALUATION ASSUMPTIONS (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	1.40%	2.50%	2.50%
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-settled appreciation rights granted	262,091	213,618	509,046
Expected life (in years)	5 years	5 years	5 years
Expected volatility	30.00%	29.00%	28.00%
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	305,269

STOCK-BASED COMPENSATION - SC_3

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED PAYMENT AWARD, PERFORMANCE-BASED AWARDS, VALUATION ASSUMPTIONS (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.40%	2.50%	2.50%

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Dec. 31, 2020USD ($)
Other Commitments [Line Items]
Letters of Credit Outstanding, Amount	$ 54.1
Guarantees
Other Commitments [Line Items]
Other Commitment	5.8
Standby Letters of Credit [Member]
Other Commitments [Line Items]
Other Commitment	6.7
Notes Payable, Other Payables | Guarantees
Other Commitments [Line Items]
Other Commitment	5.5
Line of Credit | Guarantees
Other Commitments [Line Items]
Other Commitment	$ 1

BUSINESS SEGMENTS (Details)

BUSINESS SEGMENTS (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting [Abstract]
Net sales		$ 4,128,841	$ 4,141,801	$ 2,086,706	$ 1,968,647	$ 2,099,452	$ 2,148,110	$ 2,150,088	$ 1,961,267	$ 12,325,995	$ 8,358,917	$ 8,176,601
Operating Income (Loss)		92,763	178,095	15,270	60,913	83,808	93,733	97,950	70,726	347,038	346,217	352,440
Segment Reporting Information [Line Items]
Net sales		4,128,841	4,141,801	2,086,706	1,968,647	2,099,452	2,148,110	2,150,088	1,961,267	12,325,995	8,358,917	8,176,601
Operating Income (Loss)		92,763	$ 178,095	$ 15,270	$ 60,913	83,808	$ 93,733	$ 97,950	$ 70,726	347,038	346,217	352,440
Depreciation and amortization										121,600	62,107	62,997
Payments for (Proceeds from) Productive Assets										56,671	44,067	36,210
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		11,880,214				5,017,635				11,880,214	5,017,635
EES
Segment Reporting [Abstract]
Net sales										5,479,760	4,860,541	4,878,836
Operating Income (Loss)										260,207	261,788	289,065
Segment Reporting Information [Line Items]
Net sales										5,479,760	4,860,541	4,878,836
Operating Income (Loss)										260,207	261,788	289,065
Depreciation and amortization										35,811	28,569	30,198
Payments for (Proceeds from) Productive Assets										7,081	20,405	7,487
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		3,726,855				2,523,481				3,726,855	2,523,481
CSS
Segment Reporting [Abstract]
Net sales										3,323,264	909,496	857,481
Operating Income (Loss)										217,163	43,835	34,592
Segment Reporting Information [Line Items]
Net sales										3,323,264	909,496	857,481
Operating Income (Loss)										217,163	43,835	34,592
Depreciation and amortization										37,765	7,155	7,413
Payments for (Proceeds from) Productive Assets										1,495	3,093	129
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		4,275,611				610,046				4,275,611	610,046
UBS
Segment Reporting [Abstract]
Net sales										3,522,971	2,588,880	2,440,284
Operating Income (Loss)										231,702	184,931	165,149
Segment Reporting Information [Line Items]
Net sales										3,522,971	2,588,880	2,440,284
Operating Income (Loss)										231,702	184,931	165,149
Depreciation and amortization										22,380	13,583	13,447
Payments for (Proceeds from) Productive Assets										12,834	6,460	2,235
Segment Reporting, Asset Reconciling Item [Line Items]
Assets		2,947,406				1,747,809				2,947,406	1,747,809
Corporate Segment
Segment Reporting [Abstract]
Net sales										0	0	0
Operating Income (Loss)										(362,034)	(144,337)	(136,366)
Segment Reporting Information [Line Items]
Net sales										0	0	0
Operating Income (Loss)										(362,034)	(144,337)	(136,366)
Depreciation and amortization										25,644	12,800	11,939
Payments for (Proceeds from) Productive Assets										35,261	14,109	$ 26,359
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	[1]	$ 930,342				$ 136,299				$ 930,342	$ 136,299
[1]	Total assets for Corporate primarily consist of cash and cash equivalents, deferred income taxes, fixed assets and right-of-use assets associated with operating leases.

SEGMENTS AND RELATED INFORMATIO

SEGMENTS AND RELATED INFORMATION - SCHEDULE OF REVENUE FROM EXTERNAL CUSTOMERS AND LONG LIVED ASSETS, BY GEOGRAPHICAL AREAS (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets		$ 933,862	$ 417,282
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets		693,807	315,288
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets		146,620	95,642
Other International
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	[1]	$ 93,435	$ 6,352
[1]	No individual other international country's tangible long-lived assets are material.

SELECTED QUARTERLY FINANCIAL _3

SELECTED QUARTERLY FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 4,128,841	$ 4,141,801	$ 2,086,706	$ 1,968,647	$ 2,099,452	$ 2,148,110	$ 2,150,088	$ 1,961,267	$ 12,325,995	$ 8,358,917	$ 8,176,601
Cost of goods sold	3,356,890	3,356,259	1,692,931	1,592,249	1,709,658	1,747,913	1,741,114	1,578,771	9,998,329	6,777,456	6,609,220
Gross Profit	771,951	785,542	393,775	376,398	389,794	400,197	408,974	382,496
Income from operations	92,763	178,095	15,270	60,913	83,808	93,733	97,950	70,726	347,038	346,217	352,440
Income before income taxes	19,384	104,332	(45,313)	44,441	67,587	80,225	80,643	53,606	122,842	282,061	281,025
Net income	20,288	80,038	(34,459)	34,175	52,694	64,339	63,215	41,950	100,039	222,198	225,355
Net Income (Loss) Available to Common Stockholders, Basic	$ 5,632	$ 66,167	$ (35,782)	$ 34,407	$ 53,098	$ 64,495	$ 63,464	$ 42,369	$ 70,421	$ 223,426	$ 227,343
Basic earnings per share attributable to WESCO International, Inc.	$ 0.11	$ 1.32	$ (0.84)	$ 0.82	$ 1.27	$ 1.53	$ 1.46	$ 0.94	$ 1.53	$ 5.18	$ 4.87
Diluted earnings per share attributable to WESCO International, Inc.	$ 0.11	$ 1.31	$ (0.84)	$ 0.82	$ 1.26	$ 1.52	$ 1.45	$ 0.93	$ 1.51	$ 5.14	$ 4.82
Cost of Goods Sold
Effect of Fourth Quarter Events [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount	$ 23,300								$ 18,900
Net Income
Effect of Fourth Quarter Events [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount	$ 16,700								$ 14,400

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) $ in Millions	Feb. 12, 2021USD ($)
Subsequent Event
Subsequent Event [Line Items]
Proceeds from Divestiture of Businesses	$ 52

Schedule II - Valuation and Q_3

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Anixter International [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation Allowances and Reserves, Charged to Other Accounts		$ 59,300
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount		23,909		$ 25,443	$ 24,468		$ 21,313
Valuation Allowances and Reserves, Charged to Cost and Expense		11,701		7,006	10,854
Valuation Allowances and Reserves, Charged to Other Accounts	[1]	5,160		52	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	[2]	(18,395)		(6,083)	(7,699)
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount		60,629		5,854	4,072	$ 2,518
Valuation Allowances and Reserves, Charged to Cost and Expense		1,900		1,745	1,608
Valuation Allowances and Reserves, Charged to Other Accounts		52,875	[3]	37	(54)
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction		$ 0		$ 0	$ 0
[1]	For the year ended December 31, 2020, the amount charged to other accounts relates to the acquisition of Anixter.
[2]	Includes a reduction in the allowance for expected credit losses due to the write-off of accounts receivable.
[3]	For the year ended December 31, 2020, the amount charged to other accounts includes $59.3 million that was recorded in connection with the acquisition of Anixter.