WESCO International (WCC) 10-K 27 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 26, 2019	Jun. 30, 2018
Entity Information [Line Items]
Entity Registrant Name	WESCO INTERNATIONAL INC.
Entity Central Index Key	929,008
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		45,195,593
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Public Float			$ 2,677,235,366

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 96,343	$ 117,953
Trade accounts receivable, net of allowance for doubtful accounts of $19,309 and $17,242 in 2013 and 2012, respectively	1,166,607	1,170,080
Other accounts receivable	96,984	101,229
Inventories, net	948,726	956,148
Income taxes receivable	24,873	23,250
Prepaid expenses and other current assets	52,107	40,189
Total current assets	2,385,640	2,408,849
Property, buildings and equipment, net	160,878	156,445
Intangible assets, net	316,016	367,104
Goodwill	1,722,603	1,771,877
Deferred income taxes	16,374	24,203
Other assets	3,525	6,990
Total assets	4,605,036	4,735,468
Current Liabilities:
Accounts payable	794,348	799,520
Accrued payroll and benefit costs	88,105	72,686
Short-term debt	30,785	34,075
Current portion of long-term debt	25,429	1,224
Bank overdrafts	17,818	37,644
Other current liabilities	105,461	95,820
Total current liabilities	1,061,946	1,040,969
Long-term debt, net of discount of $174,686 and $183,644 in 2013 and 2012, respectively	1,167,311	1,313,261
Deferred income taxes	143,967	136,858
Other noncurrent liabilities	102,086	128,237
Total liabilities	2,475,310	2,619,325
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.01 par value; 20,000,000 shares authorized, no shares issued or outstanding	0	0
Additional capital	993,666	999,156
Retained earnings	2,307,462	2,079,697
Treasury stock, at cost; 18,179,275 and 18,102,528 shares in 2013 and 2012, respectively	(758,018)	(647,158)
Accumulated other comprehensive income	(408,435)	(312,590)
Total WESCO International stockholders' equity	2,129,726	2,116,143
Noncontrolling interest	(5,584)	(3,596)
Total stockholders' equity	2,135,310	2,119,739
Total liabilities and stockholders' equity	4,605,036	4,735,468
Common Stock
Stockholders' Equity:
Common Stock	592	591
Common Class B
Stockholders' Equity:
Common Stock	$ 43	$ 43

CONSOLIDATED BALANCE SHEETS CON

CONSOLIDATED BALANCE SHEETS CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts	$ 24,468	$ 21,313
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 9,243	$ 14,224
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Treasury stock, shares outstanding	18,391,042	16,375,653
Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	210,000,000	210,000,000
Common stock, shares issued	59,157,696	59,045,762
Common stock, shares outstanding	45,106,085	47,009,540
Common Class B
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	4,339,431	4,339,431
Common stock, shares outstanding	0	0

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 2,011,447	$ 2,067,245	$ 2,103,994	$ 1,993,915	$ 1,996,647	$ 2,000,159	$ 1,909,624	$ 1,772,591	$ 8,176,601	$ 7,679,021	$ 7,336,017
Cost of goods sold (excluding depreciation and amortization below)	1,621,117	1,670,037	1,704,100	1,613,966	1,613,469	1,614,814	1,543,510	1,422,573	6,609,220	6,194,366	5,887,814
Selling, general and administrative expense									1,151,944	1,101,598	1,050,799
Depreciation and amortization									62,997	64,017	66,858
Revenue from Contract with Customer, Excluding Assessed Tax									8,176,601	7,679,021	7,336,017
Income from operations	90,499	97,517	91,183	73,241	81,446	89,250	83,105	67,089	352,440	319,040	330,546
Other Nonoperating Income (Expense)									(71,415)	(66,600)	(75,062)
Gain (Loss) on Extinguishment of Debt									0	0	(123,933)
Income before income taxes	73,658	80,467	73,442	53,458	63,844	71,939	66,289	50,368	281,025	252,440	131,551
Provision for income taxes									55,670	89,307	30,431
Net income	58,066	66,645	57,673	42,971	22,222	53,576	49,535	37,800	225,355	163,133	101,120
Net loss attributable to noncontrolling interest									(1,988)	(327)	(468)
Net Income attributable to WESCO International, Inc.	$ 58,133	$ 66,849	$ 57,940	$ 44,421	$ 22,546	$ 53,675	$ 49,510	$ 37,729	227,343	163,460	101,588
Comprehensive Income:
Foreign currency translation adjustment									(99,643)	85,762	38,275
Benefit plan adjustments									3,798	(6,381)	(2,485)
Comprehensive income attributable to WESCO International, Inc.									$ 131,498	$ 242,841	$ 137,378
Earnings per share :
Basic	$ 1.27	$ 1.42	$ 1.23	$ 0.94	$ 0.48	$ 1.13	$ 1.03	$ 0.77	$ 4.87	$ 3.42	$ 2.30
Diluted	$ 1.26	$ 1.41	$ 1.22	$ 0.93	$ 0.47	$ 1.12	$ 1.02	$ 0.76	$ 4.82	$ 3.38	$ 2.10
Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax									$ 23,300	$ 26,200	$ 27,100
Shipping and Handling [Member]
Cost of goods sold (excluding depreciation and amortization below)									$ 74,100	$ 61,800	$ 57,900

CONSOLIDATED STATEMENTS OF IN_2

CONSOLIDATED STATEMENTS OF INCOME Net Interest and Other (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Income Statement [Abstract]
Foreign Currency Transaction Gain (Loss), before Tax	$ 2.8

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Additional Capital	Retained Earnings (Deficit)	Treasury Stock	Noncontrolling Interest	Accumulated Other Comprehensive Income (Loss)	Common Class B	Common Stock
Common Stock, Value, Issued							$ 43	$ 586
Common Stock, Shares, Issued							4,339,431	58,597,380
Additional Paid in Capital, Common Stock	$ 1,117,421
Retained Earnings (Accumulated Deficit)	1,812,681
Treasury Stock, Value	$ (772,679)
Treasury Stock, Shares	(20,763,021)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (2,801)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(427,761)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (3,224)				$ 2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				(44,191)				(230,464)
Stock Granted, Value, Share-based Compensation, Net of Forfeitures	12,493
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options	(2,876)
Conversion of debentures, value								$ 0
Adjustments Related to Tax Withholding for Share-based Compensation		$ (1,253)	$ 488					$ 0
Conversion of debentures, shares				6,261,497				7,295
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	(139,765)
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments				$ 233,366
Shares Paid for Tax Withholding for Share Based Compensation								(17,358)
Net Income (Loss) Attributable to Noncontrolling Interest	468				$ 468
Translation adjustment						$ 38,275
Benefit plan adjustments	2,485					(2,485)
Net Income attributable to WESCO International, Inc.	101,588
Common Stock, Value, Issued							$ 43	$ 588
Common Stock, Shares, Issued							4,339,431	58,817,781
Additional Paid in Capital, Common Stock	986,020
Retained Earnings (Accumulated Deficit)	1,914,757
Treasury Stock, Value	$ (542,537)
Treasury Stock, Shares	(14,545,715)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (3,269)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(391,971)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (4,583)				$ 3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				(51,401)				(243,361)
Stock Granted, Value, Share-based Compensation, Net of Forfeitures	14,809
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options	(407)
Adjustments Related to Tax Withholding for Share-based Compensation		(1,304)	1,480					$ 0
Treasury Stock, Value, Acquired, Par Value Method		38
Treasury Stock, Value, Acquired, Cost Method	$ (100,038)
Treasury Stock, Shares, Acquired	(1,778,537)
Shares Paid for Tax Withholding for Share Based Compensation								(15,380)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 327				327
Translation adjustment						85,762
Benefit plan adjustments	6,381					(6,381)
Stockholders' equity at period end at Dec. 31, 2017	2,116,143
Net Income attributable to WESCO International, Inc.	163,460
Common Stock, Value, Issued							$ 43	$ 591
Common Stock, Shares, Issued							4,339,431	59,045,762
Additional Paid in Capital, Common Stock	999,156
Retained Earnings (Accumulated Deficit)	2,079,697
Treasury Stock, Value	$ (647,158)
Treasury Stock, Shares	(16,375,653)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (3,596)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(312,590)
Stock Issued, Value, Stock Options Exercised, Net of Tax Benefit (Expense)				$ (841)				$ 1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				(11,943)				(130,371)
Stock Granted, Value, Share-based Compensation, Net of Forfeitures	10,790
Adjustments to Additional Paid in Capital, Share-based Compensation and Exercise of Stock Options	(45)
Adjustments Related to Tax Withholding for Share-based Compensation		(1,254)	$ 422					$ 0
Treasury Stock, Value, Acquired, Par Value Method		$ (14,981)
Treasury Stock, Value, Acquired, Cost Method	$ (110,019)
Treasury Stock, Shares, Acquired	(2,003,446)
Shares Paid for Tax Withholding for Share Based Compensation								(18,437)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 1,988				$ 1,988
Translation adjustment						(99,643)
Benefit plan adjustments	(3,798)					$ 3,798
Stockholders' equity at period end at Dec. 31, 2018	2,129,726
Net Income attributable to WESCO International, Inc.	227,343
Common Stock, Value, Issued							$ 43	$ 592
Common Stock, Shares, Issued							4,339,431	59,157,696
Additional Paid in Capital, Common Stock	993,666
Retained Earnings (Accumulated Deficit)	2,307,462
Treasury Stock, Value	$ (758,018)
Treasury Stock, Shares	(18,391,042)
Stockholders' Equity Attributable to Noncontrolling Interest	$ (5,584)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (408,435)

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Parenthetical [Abstract]
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 0	$ 0	$ 67
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ 1,406	$ (2,361)	$ (302)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net income	$ 225,355	$ 163,133	$ 101,120
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,997	64,017	66,858
Stock-based compensation expense	16,445	14,809	12,493
Amortization of Debt Issuance Costs and Discounts	4,482	3,984	6,684
Gain (Loss) on Extinguishment of Debt	0	0	123,933
Other Operating Activities, Cash Flow Statement	(8,134)	(3,959)	(5,538)
Interest related to uncertain tax positions	200	100	1,200
Deferred income taxes	9,137	(50,396)	(45,174)
Changes in assets and liabilities
Increase (Decrease) in Accounts Receivable	(22,934)	(112,977)	56,767
Inventories, net	(8,702)	(119,002)	(1,612)
Increase (Decrease) in Other Operating Assets	(4,239)	(2,829)	11,579
Accounts payable	(9,193)	(102,870)	40,607
Accrued payroll and benefit costs	18,777	24,679	(1,922)
Other current and noncurrent liabilities	(5,656)	64,793	15,654
Net cash provided by operating activities	296,721	149,122	300,235
Investing Activities:
Capital expenditures	(36,210)	(21,507)	(17,957)
Acquisition payments, net of cash acquired	0	0	(50,890)
Proceeds from sale of assets	12,461	6,766	8,361
Payments for (Proceeds from) Other Investing Activities	(10,393)	9,446	(10,000)
Net cash used in investing activities	(34,142)	(5,295)	(70,486)
Financing Activities:
Proceeds from issuance of short-term debt	142,293	175,819	111,458
Repayments of short-term debt	(143,747)	(164,030)	(131,501)
Proceeds from issuance of long-term debt	1,193,067	1,504,636	2,082,738
Repayments of long-term debt	(1,318,470)	(1,556,636)	(2,323,568)
Debt issuance costs	0	(915)	(6,002)
Repurchase of common stock	(127,169)	(106,792)	(4,818)
Increase (Decrease) in Book Overdrafts	(19,857)	8,199	(4,907)
Proceeds from (Payments for) Other Financing Activities	(1,211)	(1,477)	337
Net cash provided (used) by financing activities	(275,094)	(141,196)	(276,263)
Effect of exchange rate on cash and cash equivalents	(9,095)	5,191	(3,634)
Net change in cash and cash equivalents	(21,610)	7,822	(50,148)
Cash and cash equivalents at the beginning of period	117,953	110,131	160,279
Cash and cash equivalents at the end of period	96,343	117,953	110,131
Supplemental disclosures:
Cash paid for interest	64,702	63,795	74,391
Cash paid for taxes	61,983	65,117	76,293
Non-cash investing and financing activities:
Payments to Acquire Equipment on Lease	$ 437	$ 552	$ 1,143

ORGANIZATION

ORGANIZATION	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION	1. ORGANIZATION WESCO International, Inc. ("WESCO International") and its subsidiaries (collectively, “WESCO” or the "Company"), headquartered in Pittsburgh, Pennsylvania, is a full-line distributor of electrical, industrial and communications maintenance, repair and operating ("MRO") and original equipment manufacturer ("OEM") products, construction materials, and advanced supply chain management and logistics services used primarily in the industrial, construction, utility and commercial, institutional and government markets. WESCO serves approximately 70,000 active customers globally, through approximately 500 branches and 10 distribution centers located primarily in the United States, Canada and Mexico, with operations in 15 additional countries.

ACCOUNTING POLICIES

ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	2. ACCOUNTING POLICIES Basis of Consolidation The consolidated financial statements include the accounts of WESCO International and all of its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. Correction of Prior Period Management determined that the deferred tax asset related to stock-based compensation was overstated by $5.7 million due to equity awards that had expired subsequent to the requisite service period in years 2016 and prior. In accordance with Staff Accounting Bulletin (“SAB”) No. 99, Materiality , and SAB No. 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements , management concluded that this misstatement is not material to the Company's previously issued annual and interim financial statements, and the correction of this item in the year ended December 31, 2018 is not material to the 2018 consolidated financial statements presented herein. The Company recorded an adjustment to decrease deferred income taxes and additional capital in the Consolidated Balance Sheet at December 31, 2018 . Reclassifications Effective January 1, 2018, WESCO adopted Accounting Standards Update (ASU) 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . The adoption of this ASU, as described below and in Note 13, resulted in the reclassification of amounts reported in the Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2017 and 2016 . The Consolidated Balance Sheet as of December 31, 2017 and the Consolidated Statements of Cash Flows for the years ended December 31, 2017 and 2016 include certain reclassifications to previously reported amounts to conform to the current period's presentation. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates are based on management’s best knowledge of current events and actions WESCO may undertake in the future, actual results may ultimately differ from the estimates. Revenue Recognition WESCO’s revenue arrangements generally consist of single performance obligations to transfer a promised good or service, or a combination of goods and services. Revenue is recognized when control has transferred to the customer, which is generally when the product has shipped from a WESCO facility or directly from a supplier. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. Revenue for integrated supply services is recognized over time based on hours incurred as the transfer of control occurs as the services are being performed. WESCO generally satisfies its performance obligations within a year or less. WESCO generally does not have significant financing terms associated with its contracts; payments are normally received within 60 days. There are generally no significant costs associated with obtaining customer contracts. WESCO generally passes through warranties offered by manufacturers or suppliers to its customers. Sales taxes (and value added taxes in foreign jurisdictions) collected from customers and remitted to governmental authorities are excluded from net sales. Supplier Volume Rebates WESCO receives volume rebates from certain suppliers based on contractual arrangements with such suppliers. Volume rebates are included within other accounts receivable in the Consolidated Balance Sheets, and represent the estimated amounts due to WESCO based on forecasted purchases and the rebate provisions of the various supplier contracts. The corresponding rebate income is recorded as a reduction to cost of goods sold. Receivables under the supplier rebate program were $73.5 million at December 31, 2018 and $72.7 million at December 31, 2017 . In 2018 , 2017 and 2016 , the supplier volume rebate as a percentage of net sales was 1.3% . Cash Equivalents Cash equivalents are defined as highly liquid investments with original maturities of 90 days or less when purchased. Allowance for Doubtful Accounts WESCO maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. WESCO has a systematic procedure using historical data and reasonable assumptions of collectability made at the local branch level and on a consolidated corporate basis to estimate allowances for doubtful accounts. If the financial condition of WESCO’s customers were to deteriorate, resulting in an impairment of their ability to make payments, additional allowances may be required. The allowance for doubtful accounts was $24.5 million at December 31, 2018 and $21.3 million at December 31, 2017 . The total amount recorded as selling, general and administrative expense related to bad debts was $10.9 million , $8.5 million and $5.9 million for 2018 , 2017 and 2016 , respectively. Inventories Inventories primarily consist of merchandise purchased for resale and are stated at the lower of cost and net realizable value. Cost is determined principally under the average cost method. WESCO makes provisions for obsolete or slow-moving inventories as necessary to reflect reductions in value. WESCO writes down its inventories to net realizable value based on internal factors derived from historical analysis of actual losses. WESCO uses past data to identify items in excess of 36 months supply relative to demand or movement. WESCO then analyzes the ultimate disposition of identified excess inventories as they are sold, returned to supplier, or scrapped. This historical item-by-item analysis allows WESCO to develop an estimate of the likelihood that an item identified as being in excess supply ultimately becomes obsolete. WESCO applies the estimate to inventories currently in excess of 36 months supply, and reduces the carrying value of its inventories by the derived amount. Reserves for excess and obsolete inventories were $27.6 million and $28.6 million at December 31, 2018 and 2017 , respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $9.7 million , $8.8 million and $7.3 million for 2018 , 2017 and 2016 , respectively. WESCO absorbs into the cost of inventories certain overhead expenses such as purchasing, receiving and storage and at December 31, 2018 and 2017 , $69.2 million and $70.7 million , respectively, of these costs were included in ending inventories. Property, Buildings and Equipment Property, buildings and equipment are recorded at cost. Depreciation expense is determined using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over either their respective lease terms or their estimated lives, whichever is shorter. Estimated useful lives range from five to forty years for buildings and leasehold improvements and three to ten years for furniture, fixtures and equipment. Capitalized computer software costs are amortized using the straight-line method over the estimated useful life, typically three to five years , and are reported at the lower of unamortized cost or net realizable value. Expenditures for new facilities and improvements that extend the useful life of an asset are capitalized. Ordinary repairs and maintenance are expensed as incurred. When property is retired or otherwise disposed of, the cost and the related accumulated depreciation are removed from the accounts and any resulting gains or losses are recorded and reported as selling, general and administrative expenses. Of WESCO’s $160.9 million net book value of property, buildings and equipment as of December 31, 2018 , $88.3 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 500 branches and 10 distribution centers, mitigating the risk of impairment. WESCO assesses its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of any such assets may not be fully recoverable. Changes in circumstances include technological advances, changes in the business model, capital structure, economic conditions or operating performance. The evaluation is based upon, among other things, utilization, serviceability and assumptions about the estimated future undiscounted cash flows that these assets are expected to generate. When the sum of the undiscounted cash flows is less than the carrying value of the asset or asset group, an impairment loss is recognized to the extent that carrying value exceeds fair value. Management applies its best judgment when performing these evaluations. Goodwill and Indefinite-Lived Intangible Assets Goodwill and indefinite-lived intangible assets are tested for impairment annually during the fourth quarter using information available at the end of September, or more frequently if triggering events occur, indicating that their carrying value may not be recoverable. WESCO tests for goodwill impairment on a reporting unit level and the evaluation involves comparing the fair value of each reporting unit to its carrying value. The fair values of the reporting units are determined using a combination of a discounted cash flow analysis and market multiples. Assumptions used for these fair value techniques are based on a combination of historical results, current forecasts, market data and recent economic events. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2018 and 2017 , respectively, goodwill and indefinite-lived trademarks totaled $1.8 billion and $1.9 billion . We performed our annual impairment tests of goodwill and indefinite-lived intangible assets during the fourth quarter. A possible indicator of goodwill impairment is the relationship of a company’s market capitalization to its book value. As of December 31, 2018 , our market capitalization exceeded our book value and the fair values of our reporting units exceeded their carrying values. Accordingly, there were no impairment losses identified as a result of our annual test. The determination of fair value involves significant management judgment and management applies its best judgment when assessing the reasonableness of financial projections. Fair values are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill and indefinite-lived intangible impairment tests will prove to be an accurate prediction of future results. Definite Lived Intangible Assets Definite lived intangible assets are amortized over 2 to 20 years. A portion of definite lived intangible assets related to certain customer relationships are amortized using an accelerated method whereas all other definite lived intangible assets subject to amortization use a straight-line method. In either case, the amortization method reflects the pattern in which the economic benefits of the respective assets are consumed or otherwise used. Definite lived intangible assets are tested for impairment if events or circumstances occur indicating that the respective asset might be impaired. Insurance Programs WESCO uses commercial insurance for auto, workers’ compensation, casualty and health claims, and information technology as a risk-reduction strategy to minimize catastrophic losses. The Company’s strategy involves large deductible policies where WESCO must pay all costs up to the deductible amount. WESCO estimates the reserve for these programs based on historical incident rates and costs. The assumptions included in developing this accrual include the period of time between the incurrence and payment of a claim. The total liability related to the insurance programs was $13.1 million and $13.9 million at December 31, 2018 and 2017 , respectively. Income Taxes WESCO accounts for income taxes under the asset and liability method, which requires the recognition of deferred income taxes for events that have future tax consequences. Under this method, deferred income taxes are recognized (using enacted tax laws and rates) based on the future income tax effects of differences in the carrying amounts of assets and liabilities for financial reporting and tax purposes. The effect of a tax rate change on deferred tax assets and liabilities is recognized in income in the period of change. WESCO recognizes deferred tax assets at amounts that are expected to be realized. To make such determination, management evaluates all positive and negative evidence, including but not limited to, prior, current and future taxable income, tax planning strategies and future reversals of existing temporary differences. A valuation allowance is recognized if it is “more-likely-than-not” that some or all of a deferred tax asset will not be realized. WESCO regularly assesses the realizability of deferred tax assets. WESCO accounts for uncertainty in income taxes using a "more-likely-than-not" recognition threshold. Due to the subjectivity inherent in the evaluation of uncertain tax positions, the tax benefit ultimately recognized may materially differ from the estimate. WESCO recognizes interest and penalties related to uncertain tax benefits as part of interest expense and income tax expense, respectively. The Tax Cuts and Jobs Act of 2017 (the “TCJA”) imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax"). Except for a portion of the previously taxed foreign earnings that have been repatriated, WESCO continues to assert that the remaining undistributed earnings of its foreign subsidiaries, the majority of which were subject to the transition tax, are indefinitely reinvested. WESCO believes it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without repatriating cash held by these foreign subsidiaries. Upon any future repatriation, additional income taxes may be incurred; however, it is not practicable to determine the amount at this time. The provisions of the TCJA also introduced U.S. taxation on certain global intangible low-taxed income ("GILTI"). WESCO has elected to account for GILTI tax as a component of income tax expense. Future adjustments (if any) resulting from additional regulatory guidance regarding the accounting for the income tax effects of TCJA will be recognized as discrete income tax expense or benefit in the period in which guidance is issued. Foreign Currency The local currency is the functional currency for the majority of WESCO’s operations outside the United States. Assets and liabilities of these operations are translated to U.S. dollars at the exchange rate in effect at the end of each period. Income statement accounts are translated at an exchange rate that approximates the average for the period. Translation adjustments arising from the use of differing exchange rates from period to period are included as a component of other comprehensive income (loss) within stockholders’ equity. Gains and losses from foreign currency transactions are included in net income for the period. Defined Benefit Pension Plan Liabilities and expenses for pension benefits are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated cash flows, the expected long-term rate of return on plan assets, and several assumptions relating to the employee workforce (salary increases, retirement age, and mortality). Fair Value of Financial Instruments The Company measures the fair value of financial assets and liabilities according to a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value and requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible at the measurement date; Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, and Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to measurements involving significant unobservable inputs (Level 3). Recently Adopted Accounting Pronouncements Effective January 1, 2018, WESCO adopted ASU 2014-09, Revenue from Contracts with Customers , and all the related amendments (“Topic 606”) using the modified retrospective approach to all open contracts (see Note 3 below). There was no impact to WESCO’s previously reported consolidated financial statements and WESCO does not expect the adoption of Topic 606 to have a material impact on its revenue and results of operations on an ongoing basis. In August 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (a consensus of the Emerging Issues Task Force) . This ASU provided guidance on eight specific cash flow issues where there was diversity in practice. The Company adopted this ASU in the first quarter of 2018. The adoption of this guidance did not have an impact on the consolidated financial statements and notes presented herein. In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, which eliminates Step 2 of the goodwill impairment test. Under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit to its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity should apply the amendments in this ASU on a prospective basis. This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Management adopted this ASU in the fourth quarter of 2018 when the Company performed its annual impairment tests. The adoption of this accounting standard did not have an impact on the consolidated financial statements and notes presented herein. In March 2017, the FASB issued ASU 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . This ASU requires that an employer disaggregate the service cost from the other components of net benefit cost. The Company adopted this guidance on a retrospective basis in the first quarter of 2018. See Note 13 for a description of the impact of this accounting standard on the Consolidated Statements of Income and Comprehensive Income presented herein. The adoption of this guidance did not have an impact on the Company's Consolidated Balance Sheets and the Consolidated Statements of Cash Flows presented herein. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting. This ASU clarifies when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The Company adopted this ASU in the first quarter of 2018. The adoption of this guidance did not have an impact on the consolidated financial statements presented and notes herein. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases , a comprehensive new standard that amends various aspects of existing accounting guidance for leases, including the recognition of a right-of-use asset and a lease liability in the balance sheet and disclosing key information about leasing arrangements. This ASU is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. During 2018, the FASB issued additional ASUs that address implementation issues and correct or improve certain aspects of the new accounting guidance for leases, including ASU 2018-10, Codification Improvements to Topic 842, Leases and ASU 2018-11, Leases (Topic 842): Targeted Improvements. These ASUs do not change the core principles in the leasing standard outlined above. The amendments in ASU 2018-11 provide an optional transition method that allows entities to initially apply the new lease standard at the adoption date. Consequently, an entity’s reporting for the comparative periods will continue to be in accordance with current lease accounting guidance. During 2018, management established a cross-functional team to evaluate and implement the new standard. The team selected a third-party software solution to facilitate the accounting and financial reporting requirements of the new lease standard. Lease data elements have been gathered and migrated to the software solution. The new standard will be adopted in the first quarter of 2019. The Company expects to use the optional transition method and elect the package of practical expedients permitted under the transition guidance. The Company also expects to elect the practical expedient related to lease and nonlease components. The Company anticipates recording right-of-use assets and lease liabilities of $200 million to $250 million in the Consolidated Balance Sheet as of January 1, 2019, most of which will relate to real estate. The Company does not expect the adoption to have a material impact on the Consolidated Statement of Income and Comprehensive Income (Loss) or Consolidated Statement of Cash Flow. The Company is currently updating business processes and internal controls to meet the standard’s new accounting, reporting and disclosure requirements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which introduces new guidance for the accounting for credit losses on certain financial instruments. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement , which amends the disclosure requirements for recurring and nonrecurring fair value measurements by removing, modifying and adding certain disclosures. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans , which amends the disclosure requirements for all employers that sponsor defined benefit pension and other post retirement plans by removing and adding certain disclosures. The amendments in this ASU are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. 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.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	. GOODWILL AND INTANGIBLE ASSETS Goodwill The following table sets forth the changes in the carrying value of goodwill: Year Ended December 31, 2018 2017 (In thousands) Beginning balance January 1 $ 1,771,877 $ 1,730,950 Foreign currency exchange rate changes (49,274 ) 40,927 Ending balance December 31 $ 1,722,603 $ 1,771,877 Intangible Assets The components of intangible assets are as follows: December 31, 2018 December 31, 2017 Life Gross Carrying Amount (1) Accumulated Amortization (1) Net Carrying Amount Gross Carrying Amount (1) Accumulated Amortization (1) Net Carrying Amount (In thousands) Intangible assets: Trademarks Indefinite $ 96,260 $ — $ 96,260 $ 100,249 $ — $ 100,249 Trademarks 4-15 25,185 (7,585 ) 17,600 25,118 (5,516 ) 19,602 Non-compete agreements 2-7 196 (141 ) 55 196 (102 ) 94 Customer relationships 2-20 358,620 (180,395 ) 178,225 377,270 (161,711 ) 215,559 Distribution agreements 10-19 36,984 (22,562 ) 14,422 39,515 (22,200 ) 17,315 Patents 10 48,310 (38,856 ) 9,454 48,310 (34,025 ) 14,285 $ 565,555 $ (249,539 ) $ 316,016 $ 590,658 $ (223,554 ) $ 367,104 (1) Excludes the original cost and related accumulated amortization of fully-amortized intangible assets. Amortization expense related to intangible assets totaled $35.9 million , $37.8 million and $39.1 million for the years ended December 31, 2018 , 2017 and 2016 , 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) 2019 $ 35,269 2020 33,417 2021 25,809 2022 23,431 2023 22,877 Thereafter 78,953

CONCENTRATIONS OF CREDIT RISK A

CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS	12 Months Ended
	Dec. 31, 2018
Risks and Uncertainties [Abstract]
CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS	6. CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS WESCO distributes its products and services and extends credit to a large number of customers in the industrial, construction, utility, and commercial, institutional and government markets. Based upon WESCO’s broad customer base, the Company has concluded that it has no material credit risk as a result of customer concentration. WESCO is subject to supplier concentration risk as Eaton Corporation, the Company's largest supplier, accounted for approximately 11% of its purchases in 2018 , 2017 and 2016 .

ACQUISITIONS

ACQUISITIONS	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
ACQUISITIONS	7. ACQUISITIONS The following table sets forth the consideration paid for acquisitions: Year Ended December 31, 2016 (In thousands) Fair value of assets acquired $ 76,980 Fair value of liabilities assumed 25,058 Cash paid for acquisitions $ 51,922 Supplemental cash flow disclosure related to acquisitions: Cash paid for acquisitions $ 51,922 Less: cash acquired (1,032 ) Cash paid for acquisitions, net of cash acquired $ 50,890 Atlanta Electrical Distributors, LLC On March 14, 2016 , WESCO Distribution, Inc. ("WESCO Distribution") completed the acquisition of Atlanta Electrical Distributors, LLC , an Atlanta-based electrical distributor focused on the construction and MRO markets from five locations in Georgia with approximately $85 million in annual sales. WESCO Distribution funded the purchase price paid at closing with borrowings under its revolving credit facility. The purchase price was allocated to the respective assets and liabilities based upon their estimated fair values as of the acquisition date. In addition to the cash paid at closing, the purchase price included a contingent payment that may be earned upon the achievement of certain financial performance targets over three consecutive one year periods. The fair value of the contingent consideration was determined using a probability-weighted outcome analysis and Level 3 inputs such as internal forecasts. This amount was initially accrued at the maximum potential payout under the terms of the purchase agreement and was reduced in 2017 to reflect a payout that aligns with current financial performance. The fair value of intangibles was estimated by management and the allocation resulted in intangible assets of $21.8 million and goodwill of $30.0 million . The intangible assets include customer relationships of $15.8 million amortized over 13 and 14 years, a trademark of $6.0 million amortized over 13 years , and non-compete agreements of less than $0.1 million amortized over 5 years . No residual value was estimated for the intangible assets being amortized. The majority of goodwill is deductible for tax purposes.

PROPERTY, BUILDINGS AND EQUIPME

PROPERTY, BUILDINGS AND EQUIPMENT	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 (In thousands) Buildings and leasehold improvements $ 111,510 $ 117,894 Furniture, fixtures and equipment 186,523 183,801 Software costs 115,631 103,842 413,664 405,537 Accumulated depreciation and amortization (291,811 ) (278,455 ) 121,853 127,082 Land 23,996 25,814 Construction in progress 15,029 3,549 $ 160,878 $ 156,445 Depreciation expense was $17.3 million , $16.3 million and $17.1 million , and capitalized software amortization was $9.8 million , $9.9 million and $10.6 million , in 2018 , 2017 and 2016 , respectively. The unamortized software cost was $24.2 million and $22.4 million as of December 31, 2018 and 2017 , respectively. Furniture, fixtures and equipment include capitalized leases of $9.3 million and $10.6 million and related accumulated amortization of $8.4 million and $9.0 million as of December 31, 2018 and 2017 , respectively.

DEBT

DEBT	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
DEBT	9. DEBT The following table sets forth WESCO’s outstanding indebtedness: As of December 31, 2018 2017 (In thousands) International lines of credit $ 30,785 $ 34,075 Term Loan Facility, less debt discount of $156 and $513 in 2018 and 2017, respectively 24,594 84,237 Accounts Receivable Securitization Facility 275,000 380,000 Revolving Credit Facility 51,598 12,000 5.375% Senior Notes due 2021 500,000 500,000 5.375% Senior Notes due 2024 350,000 350,000 Capital leases 1,123 1,959 Total debt 1,233,100 1,362,271 Less unamortized debt issuance costs (9,575 ) (13,711 ) Less short-term debt and current portion of long-term debt (56,214 ) (35,299 ) Total long-term debt $ 1,167,311 $ 1,313,261 International Lines of Credit Certain foreign subsidiaries of WESCO have entered into uncommitted lines of credit, which serve as overdraft facilities, to support local operations. The maximum borrowing limit varies by facility and ranges between $2.0 million and $21.0 million . The applicable interest rate for borrowings under these lines of credit varies by country and is governed by the applicable loan agreement. The international lines of credit are renewable on an annual basis and certain facilities are fully and unconditionally guaranteed by WESCO Distribution. Accordingly, borrowings under these lines directly reduce availability under the Revolving Credit Facility. The average interest rate for these facilities was 8.78% and 5.42% at December 31, 2018 and 2017 , respectively. Term Loan Facility On December 12, 2012 , WESCO Distribution, as U.S. borrower, WDCC Enterprises Inc. ("WDCC" and together with WESCO Distribution, the “Borrowers”), as Canadian borrower, and WESCO International entered into a Term Loan Agreement (the “Term Loan Agreement”) among WESCO Distribution, WDCC, the Company, the lenders party thereto and Credit Suisse AG Cayman Islands Branch, as administrative agent and as collateral agent. The Term Loan Agreement provided a seven-year term loan facility (the “Term Loan Facility”), which consisted of two separate sub-facilities: (i) a Canadian sub-facility in an aggregate principal amount of CAD 150 million , issued at a 2.0% discount, and (ii) a U.S. sub-facility in an aggregate principal amount of $700 million , issued at a 1.0% discount. The proceeds of the Term Loan Facility were used to finance the acquisition of EECOL, and to pay fees and expenses incurred in connection with the acquisition and certain other transactions. Subject to the terms of the Term Loan Agreement, the Borrowers may request incremental term loans from time to time in an aggregate principal amount not to exceed at any time $300 million , with an equivalent principal amount in U.S. dollars being calculated for any incremental term loan denominated in Canadian dollars. On November 19, 2013, the Borrowers and WESCO International entered into an amendment (the “Term Loan Amendment”) to the Term Loan Agreement. The Term Loan Amendment, among other things, reduced the applicable margin on U.S. term loans by 0.50% and the LIBOR floor applicable to the U.S. sub-facility from 1.00% to 0.75%. The modified pricing terms were effective December 13, 2013. On November 26, 2013, WESCO Distribution sold $500 million aggregate principal amount of 5.375% Senior Notes due 2021 (the “2021 Notes”), and used the net proceeds plus excess cash to prepay $500 million under the Company's U.S. sub-facility of the Term Loan Facility (see discussion below under “5.375% Senior Notes due 2021” for additional information). The prepayment satisfied all remaining quarterly repayment obligations under the U.S. sub-facility. As of December 31, 2018 , the amount outstanding under the U.S. sub-facility was $24.8 million . The Canadian sub-facility was fully repaid in 2015 using cash provided by Canadian operations. Borrowings under the Term Loan Facility bear interest at base rates plus applicable margins. At December 31, 2018 , the interest rate on borrowings under the U.S. sub-facility was 7.5% . To the extent not previously paid, the outstanding U.S. sub-facility will become due and payable on December 12, 2019, with any unpaid incremental term loans becoming due and payable on the respective maturity dates applicable to those incremental term loans. At any time or from time to time, the Borrowers may prepay borrowings under the Term Loan Facility in whole or in part without premium or penalty. The Borrowers' obligations under the Term Loan Facility are secured by substantially all of the assets of the Borrowers, the Company and certain of the Company's other subsidiaries; provided that, with respect to borrowings under the U.S. sub-facility, the collateral does not include assets of certain foreign subsidiaries or more than 65% of the issued and outstanding equity interests in certain foreign subsidiaries. The Term Loan Facility contains customary affirmative and negative covenants for credit facilities of this type. The Term Loan Facility also provides for customary events of default. Accounts Receivable Securitization Facility On November 8, 2017, WESCO Distribution amended its accounts receivable securitization facility (the "Receivables Facility") pursuant to the terms and conditions of a Fifth Amendment to Fourth Amended and Restated Receivables Purchase Agreement, by and among WESCO Receivables Corp. (“WESCO Receivables”), WESCO Distribution, the various purchasers from time to time party thereto and PNC Bank, National Association, as Administrator (the "Amendment"). The Amendment extended the term of the Receivables Facility to September 24, 2020 and added and amended certain other defined terms. Substantially all other terms and conditions of the Receivables Facility were unchanged. The Receivables Facility has a purchase limit of $550 million with the opportunity to exercise an accordion feature that permits increases in the purchase limit of up to $100 million . The interest rate spread and commitment fee of the Receivables Facility is 0.95% and 0.45% , respectively. Under the Receivables Facility, WESCO sells, on a continuous basis, an undivided interest in all domestic accounts receivable to WESCO Receivables, a wholly owned special purpose entity (the “SPE”). The SPE sells, without recourse, a senior undivided interest in the receivables to financial institutions for cash while maintaining a subordinated undivided interest in the receivables, in the form of overcollateralization. Since WESCO maintains control of the transferred receivables, the transfers do not qualify for “sale” treatment. As a result, the transferred receivables remain on the balance sheet, and WESCO recognizes the related secured borrowing. WESCO has agreed to continue servicing the sold receivables for the third-party conduits and financial institutions at market rates; accordingly, no servicing asset or liability has been recorded. The expenses associated with the Receivables Facility are reported as a component of net interest and other in the Consolidated Statements of Income and Comprehensive Income. As of December 31, 2018 and 2017 , accounts receivable eligible for securitization totaled $758.3 million and $751.2 million , respectively. The Consolidated Balance Sheets as of December 31, 2018 and 2017 include $275.0 million and $380.0 million , respectively, of account receivable balances legally sold to third parties, as well as borrowings for equal amounts. At December 31, 2018 , the interest rate for this facility was approximately 2.0% . Revolving Credit Facility On September 24, 2015, WESCO International, WESCO Distribution and certain other subsidiaries of the Company entered into a $600 million revolving credit facility (the “Revolving Credit Facility”), which contains a letter of credit sub-facility of up to $125 million, pursuant to the terms and conditions of a Second Amended and Restated Credit Agreement (the "Credit Agreement"). The Revolving Credit Facility contains an accordion feature allowing WESCO Distribution to request increases to the borrowing commitments of up to $200 million in the aggregate, subject to customary conditions. The Revolving Credit Facility matures in September 2020 and consists of two separate sub-facilities: (i) a Canadian sub-facility with a borrowing limit of up to $400 million , which is collateralized by substantially all assets of WESCO Canada and the other Canadian Borrowers, other than, among other things, real property, in each case, subject to customary exceptions and limitations, and (ii) a U.S sub-facility with a borrowing limit of up to $600 million less the amount of outstanding borrowings under the Canadian sub-facility. The U.S. sub-facility is collateralized by substantially all assets of WESCO Distribution and its domestic subsidiaries which are party to the Credit Agreement, other than, among other things, real property and accounts receivable sold or intended to be sold pursuant to the Receivables Purchase Agreement. 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 1.75% for LIBOR-based borrowings and 0.25% and 0.75% for prime rate-based borrowings. At December 31, 2018 , the interest rate for this facility was approximately 3.5% . The Credit Agreement requires ongoing compliance with certain customary affirmative and negative covenants. The Credit Agreement also contains customary events of default. During 2018 , WESCO borrowed $473.1 million under the Revolving Credit Facility and made repayments in the aggregate amount of $433.5 million . During 2017 , aggregate borrowings and repayments were $834.4 million and $826.4 million , respectively. WESCO had $515.9 million available under the Revolving Credit facility at December 31, 2018 , after giving effect to $27.2 million of outstanding letters of credit, $19.5 million of surety bonds, and $5.3 million of other reserves, as compared to $562.9 million available under the Revolving Credit facility at December 31, 2017 , after giving effect to $18.0 million of outstanding letters of credit, $19.1 million of surety bonds, and $7.1 million of other reserves. 5.375% Senior Notes due 2021 In November 2013, WESCO Distribution issued $500 million aggregate principal amount of 2021 Notes through a private offering exempt from the registration requirements of the Securities Act of 1933, as amended (the “Securities Act”). The 2021 Notes were issued at 100% of par and are governed by an indenture (the “2021 Indenture”) entered into on November 26, 2013 between WESCO International and U.S. Bank National Association, as trustee. The 2021 Notes are unsecured senior obligations of WESCO Distribution and are guaranteed on a senior unsecured basis by WESCO International. The 2021 Notes bear interest at a stated rate of 5.375% , payable semi-annually in arrears on June 15 and December 15 of each year. In addition, WESCO incurred costs related to the issuance of the 2021 Notes totaling $8.4 million , which were recorded as a reduction to the carrying value of the debt and are being amortized over the life of the notes. The 2021 Notes mature on December 15, 2021. The net proceeds of the 2021 Notes were used to prepay a portion of the U.S. sub-facility of the term loans due 2019. Under the terms of a registration rights agreement dated as of November 26, 2013 among WESCO Distribution, WESCO International and Merrill Lynch, Pierce, Fenner & Smith Incorporated, as the representative of the initial purchasers of the 2021 Notes, WESCO Distribution and WESCO International agreed to register under the Securities Act notes having terms identical in all material respects to the 2021 Notes (the “2021 Exchange Notes”) and to make an offer to exchange the 2021 Exchange Notes for the 2021 Notes. WESCO Distribution launched the exchange offer on June 12, 2014 and the exchange offer expired on July 17, 2014. At any time WESCO Distribution may redeem all or a part of the 2021 Notes. Between December 15, 2018 and December 14, 2019, WESCO Distribution may redeem all or a part of the 2021 Notes at a redemption price equal to 101.344% of the principal amount. On and after December 15, 2019, WESCO Distribution may redeem all or a part of the 2021 Notes at a redemption price equal to 100% of the principal amount. The 2021 Indenture contains customary covenants and customary events of default. In addition, upon a change of control, the holders of 2021 Notes have the right to require WESCO Distribution to repurchase all or any part of the 2021 Notes at a redemption price equal to 101% of the principal amount, plus accrued and unpaid interest. 5.375% Senior Notes due 2024 In June 2016, WESCO Distribution issued $350 million aggregate principal amount of 5.375% Senior Notes due 2024 (the "2024 Notes") through a private offering exempt from the registration requirements of the Securities Act. The 2024 Notes were issued at 100% of par and are governed by an indenture (the “2024 Indenture”) entered into on June 15, 2016 among WESCO Distribution, as issuer, WESCO International, as parent guarantor, and U.S. Bank National Association, as trustee. The 2024 Notes are unsecured senior obligations of WESCO Distribution and are guaranteed on a senior unsecured basis by WESCO International. The 2024 Notes bear interest at a rate of 5.375% per annum, payable semi-annually in arrears on June 15 and December 15 of each year. WESCO incurred costs totaling $6.0 million to issue the 2024 Notes, which were recorded as a reduction to the carrying value of the debt and are being amortized over the life of the note. The notes mature on June 15, 2024. The Company used the net proceeds to redeem its 6.0% Convertible Senior Debentures due 2029 (the "2029 Debentures") on September 15, 2016. Under the terms of a registration rights agreement dated as of June 15, 2016 among WESCO Distribution, as the issuer, WESCO International, as parent guarantor, and Goldman, Sachs & Co., as representative of the initial purchasers of the 2024 Notes, WESCO Distribution and WESCO International agreed to register under the Securities Act notes having terms identical in all material respects to the 2024 Notes (the “2024 Exchange Notes”) and to make an offer to exchange the 2024 Exchange Notes for the 2024 Notes. WESCO Distribution launched the exchange offer on December 28, 2016 and the exchange offer expired on January 31, 2017. At any time on or after June 15, 2019, WESCO Distribution may redeem all or a part of the 2024 Notes. Between June 15, 2019 and June 14, 2020, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 104.031% of the principal amount. Between June 15, 2020 and June 14, 2021, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 102.688% of the principal amount. Between June 15, 2021 and June 14, 2022, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 101.344% of the principal amount. On and after June 15, 2022, WESCO Distribution may redeem all or a part of the 2024 Notes at a redemption price equal to 100% of the principal amount. The 2024 Indenture contains customary covenants and events of default. Upon a change of control, the holders of the 2024 Notes have the right to require WESCO Distribution to repurchase all or any part of the 2024 Notes at a redemption price equal to 101% of the principal amount thereof, plus accrued and unpaid interest. 6.0% Convertible Senior Debentures due 2029 On August 27, 2009, WESCO International completed an exchange offer pursuant to which it issued $345 million in aggregate principal amount of the 2029 Debentures. On September 15, 2016 , the Company redeemed the 2029 Debentures. Holders of the 2029 Debentures received cash totaling $344.8 million , which was equal to the principal amount of the then-outstanding debentures, in addition to accrued and unpaid interest. Holders who surrendered the 2029 Debentures for conversion received 18 shares of WESCO stock for each $1,000 principal amount of 2029 Debentures converted. In total, 6,267,688 shares were issued on the redemption date. The redemption resulted in a non-cash loss of $123.9 million , which included the write off of unamortized debt issuance costs. WESCO separately accounted for the liability and equity components of its 2029 Debentures in a manner that reflected its non-convertible debt borrowing rate. WESCO utilized an interest rate of 13.875% to reflect the non-convertible debt borrowing rate of its offering upon issuance, which was determined based on discussions with its financial institutions and a review of relevant market data, and resulted in a $181.2 million discount to the 2029 Debenture balance and a net increase in additional capital of $106.5 million . In addition, the financing costs incurred to issue the 2029 Debentures were allocated between the instrument's debt and equity components. The debt discount was amortized to interest expense, using the effective interest method, over the implicit life of the debentures. WESCO amortized the financing costs on a straight-line basis over the term of the instrument. For the year ended December 31, 2016 , non-cash interest expense for the amortization of the debt discount and debt issuance costs was $3.1 million . 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, 2018 and 2017 , unamortized debt issuance costs of $9.6 million and $13.7 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, 2018 . The following table sets forth the aggregate principal repayment requirements for all indebtedness for the next five years and thereafter, as of December 31, 2018 : (In thousands) 2019 $ 56,702 2020 326,554 2021 500,000 2022 — 2023 — Thereafter 350,000 Total payments on debt 1,233,256 Debt discount (156 ) Total debt $ 1,233,100 WESCO’s credit agreements contain various restrictive covenants that, among other things, impose limitations on: (i) dividend payments or certain other restricted payments or investments; (ii) the incurrence of additional indebtedness and guarantees; (iii) creation of liens; (iv) mergers, consolidation or sales of substantially all of WESCO’s assets; (v) certain transactions among affiliates; (vi) payments by certain subsidiaries to WESCO, and (vii) capital expenditures. In addition, the Revolving Credit Facility and the Receivables Facility require WESCO to meet certain fixed charge coverage tests depending on availability or liquidity, respectively.

CAPITAL STOCK

CAPITAL STOCK	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
CAPITAL STOCK	10. CAPITAL STOCK Preferred Stock There are 20 million shares of preferred stock authorized at a par value of $0.01 per share; there are no shares issued or outstanding. The Board of Directors has the authority, without further action by the stockholders, to issue all authorized preferred shares in one or more series and to fix the number of shares, designations, voting powers, preferences, optional and other special rights and the restrictions or qualifications thereof. The rights, preferences, privileges and powers of each series of preferred stock may differ with respect to dividend rates, liquidation values, voting rights, conversion rights, redemption provisions and other matters. Common Stock There are 210 million shares of common stock and 20 million shares of Class B common stock authorized at a par value of $0.01 per share. The Class B common stock is identical to the common stock, except for voting and conversion rights. The holders of Class B common stock have no voting rights. With certain exceptions, Class B common stock may be converted, at the option of the holder, into the same number of shares of common stock. The terms of the Revolving Credit Facility and the Term Loan Facility, as well as the indentures governing the 2021 Notes and 2024 Notes, place certain limits on the Company's ability to declare or pay dividends and repurchase common stock. The share repurchases in 2018 and 2017 , as described in Note 12, were made within the limits of our various credit agreements. At December 31, 2018 and 2017 , no dividends had been declared and, therefore, no retained earnings were reserved for dividend payments. Treasury Stock Common stock purchased for treasury is recorded at cost. At the date of subsequent reissue, the treasury stock account is reduced by the cost of such stock, with cost determined on a weighted-average basis.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	11. INCOME TAXES The Tax Cuts and Jobs Act of 2017 (the "TCJA”), enacted on December 22, 2017, provided a broad range of change to U.S. corporate tax law, including changes to the U.S. corporate income tax rate, new business-related exclusions, deductions and credits, as well as international tax provisions. Most notably, the TCJA permanently reduced the U.S. corporate income tax rate from 35% to 21%, effective January 1, 2018, and imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax"). The TCJA also introduced anti-base erosion provisions, including the global intangible low-taxed income ("GILTI") tax. As a result of the reduction in the U.S. corporate income tax rate, the Company remeasured its U.S. deferred income tax balances and recorded a provisional deferred income tax benefit of $56.4 million for the year ended December 31, 2017 . The Company also recognized provisional current income tax expense for the transition tax under the TCJA of $82.8 million for the year ended December 31, 2017 . After the utilization of foreign tax credit carryforwards of $17.8 million , a provisional liability of $65.0 million was accrued for the transition tax as of December 31, 2017 , which is payable over a period of eight years. During the year ended December 31, 2018 , the Company completed its accounting for the income tax effects of the TCJA, which resulted in an additional deferred income tax benefit of $0.9 million and a discrete benefit of $3.4 million . As of December 31, 2018 , a liability of $43.2 million was in the Consolidated Balance Sheet for the transition tax. The accounting for the income tax effects of the TCJA was completed based on regulatory guidance issued to date. Additional guidance could be issued, which could affect the amounts described above. Future adjustments (if any) will be recognized as discrete income tax expense or benefit in the period in which guidance is issued. The following table sets forth the components of income before income taxes by jurisdiction: Year Ended December 31, 2018 2017 2016 (In thousands) United States $ 198,556 $ 180,957 $ 80,881 Foreign 82,469 71,483 50,670 Income before income taxes $ 281,025 $ 252,440 $ 131,551 The following table sets forth the components of the provision (benefit) for income taxes: Year Ended December 31, 2018 2017 2016 (In thousands) Current income taxes: Federal (1) $ 28,464 $ 122,170 $ 65,614 State 7,458 2,259 6,489 Foreign 10,611 15,274 3,502 Total current income taxes 46,533 139,703 75,605 Deferred income taxes: Federal 5,253 (48,060 ) (42,835 ) State 1,967 4,508 (2,938 ) Foreign 1,917 (6,844 ) 599 Total deferred income taxes 9,137 (50,396 ) (45,174 ) Provision for income taxes $ 55,670 $ 89,307 $ 30,431 (1) Income tax expense related to stock-based awards and other equity instruments recorded directly to additional paid in capital totaled $0.1 million in 2016 . Due to the adoption of ASU 2016-09 in the first quarter of 2017 , there was no income tax expense or benefit recorded to additional paid in capital for stock-based awards in 2018 and 2017 . The following table sets forth the reconciliation between the federal statutory income tax rate and the effective tax rate: Year Ended December 31, 2018 2017 2016 Federal statutory rate 21.0 % 35.0 % 35.0 % State income taxes, net of federal income tax benefit 2.8 1.4 1.0 Deemed repatriation of undistributed foreign earnings (1.2 ) 32.8 — Deferred income tax remeasurement (0.3 ) (22.4 ) — Tax effect of intercompany financing (5.6 ) (10.5 ) (19.9 ) Other (1) 3.1 (0.9 ) 7.0 Effective tax rate 19.8 % 35.4 % 23.1 % (1) Certain components of the effective tax rate for 2017 and 2016 have been reclassified to conform to the current period presentation. As a result of the TCJA, WESCO reevaluated its intent and ability to repatriate foreign earnings based upon the liquidity of the Company's domestic operations and cash flow needs of its foreign subsidiaries. Consequently, during the year ended December 31, 2018 , WESCO repatriated a portion of the previously taxed earnings attributable to the Company's Canadian operations to repay outstanding indebtedness in the U.S. WESCO continues to assert that the remaining undistributed earnings of its foreign subsidiaries, the majority of which were subject to the transition tax described above, are indefinitely reinvested. WESCO believes that it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without repatriating cash held by these foreign subsidiaries. Upon any future repatriation, additional income taxes may be incurred; however, it is not practicable to determine the amount at this time. The following table sets forth deferred tax assets and liabilities: As of December 31, 2018 2017 (In thousands) Assets Liabilities Assets Liabilities Accounts receivable $ 3,657 $ — $ 3,496 $ — Inventories — 3,315 — 3,181 Depreciation of property, buildings and equipment — 17,384 — 13,283 Amortization of intangible assets — 158,795 — 159,107 Employee benefits 20,107 — 14,835 — Stock-based compensation (1) 12,840 — 16,341 — Advance payments — — 8,456 — Tax loss carryforwards 15,557 — 19,128 — Other 7,927 4,115 11,850 8,672 Deferred income taxes before valuation allowance 60,088 183,609 74,106 184,243 Valuation allowance (4,072 ) — (2,518 ) — Total deferred income taxes $ 56,016 $ 183,609 $ 71,588 $ 184,243 (1) The Company does not expect the executive compensation deduction rules in Section 162(m) of the Internal Revenue Code as amended by the TCJA to have a material impact on the realizability of the deferred tax asset related to stock-based compensation. As of December 31, 2018 and 2017 , WESCO had deferred tax assets of $6.4 million and $10.4 million , respectively, related to Canadian net operating loss carryforwards. The Canadian net operating loss carryforwards expire beginning in 2036 through 2037 . Additionally, WESCO had deferred tax assets of $7.2 million and $7.0 million as of December 31, 2018 and 2017 , respectively, related to non-Canadian foreign net operating loss carryforwards. These net operating loss carryforwards expire beginning in 2019 through 2028 , while some may be carried forward indefinitely. As of December 31, 2018 and 2017 , WESCO had deferred tax assets of $3.2 million and $3.1 million , respectively, related to state net operating loss carryforwards. These carryforwards expire beginning in 2022 through 2037 . The Company has determined, based upon an evaluation of all available evidence, that it "more-likely-than-not" will utilize all of its net operating loss carryforwards before expiration, other than those incurred in certain non-Canadian foreign jurisdictions. Accordingly, the Company recorded a full valuation allowance against deferred tax assets related to certain non-Canadian foreign net operating loss carryforwards of $4.1 million and $2.5 million at December 31, 2018 and 2017 , respectively. The Company is under examination by tax authorities in the U.S. and Canada and remains subject to examination until the applicable statutes of limitation expire. The statutes of limitation for the material jurisdictions in which the Company files income tax returns remain open principally due to certain transfer pricing matters and are as follows: United States — Federal 2004 and forward United States — Material States 2004 and forward Canada 2004 and forward The following table sets forth the reconciliation of gross unrecognized tax benefits: As of December 31, 2018 2017 2016 (In thousands) Beginning balance January 1 $ 4,348 $ 6,181 $ 5,436 Additions for tax positions of prior years — — 3,298 Reductions for tax positions of prior years — (155 ) (21 ) Settlements (2,646 ) (1,025 ) (1,921 ) Lapse in statute of limitations (287 ) (755 ) (728 ) Foreign currency exchange rate changes (122 ) 102 117 Ending balance December 31 $ 1,293 $ 4,348 $ 6,181 The total amount of unrecognized tax benefits were $1.3 million , $4.3 million , and $6.2 million as of December 31, 2018 , 2017 and 2016 , respectively. The amount of unrecognized tax benefits that would affect the effective tax rate if recognized in the consolidated financial statements was $1.3 million , $1.7 million , and $7.5 million , respectively. It is reasonably possible that the amount of unrecognized tax benefits will decrease by approximately $0.1 million within the next twelve months due to the settlement of uncertain tax positions related to state audits or the expiration of statutes of limitation. This amount could affect the effective tax rate if recognized in the consolidated financial statements. The Company classifies interest related to unrecognized tax benefits as a component of net interest and other in the Consolidated Statement of Income and Comprehensive Income. Interest expense on unrecognized tax benefits was $0.2 million , $0.1 million , and $1.2 million for 2018 , 2017 and 2016 , respectively. As of December 31, 2018 and 2017 , WESCO had a liability of $0.8 million and $1.8 million , respectively, for interest expense related to unrecognized tax benefits. The Company classifies penalties related to unrecognized tax benefits as part of income tax expense. Penalties recorded in income tax expense were immaterial in 2018 , 2017 , and 2016 .

EARNINGS PER SHARE EARNINGS PER

EARNINGS PER SHARE EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
EARNINGS PER SHARE	12. EARNINGS PER SHARE Basic earnings per share is computed by dividing net income attributable to WESCO International by the weighted-average number of common shares outstanding during the periods. Diluted earnings per share is computed by dividing net income attributable to WESCO International by the weighted-average common shares and common share equivalents outstanding during the periods. The dilutive effect of common share equivalents is considered in the diluted earnings per share computation using the treasury stock method, which includes consideration of equity awards and contingently convertible debt. The following tables set forth the details of basic and diluted earnings per share: Year Ended December 31, 2018 2017 2016 (In thousands, except per share data) Net income attributable to WESCO International $ 227,343 $ 163,460 $ 101,588 Weighted-average common shares outstanding used in computing basic earnings per share 46,722 47,849 44,116 Common shares issuable upon exercise of dilutive equity awards 477 512 543 Common shares issuable from contingently convertible debentures (see below for basis of calculation) — — 3,674 Weighted-average common shares outstanding and common share equivalents used in computing diluted earnings per share 47,199 48,361 48,333 Earnings per share attributable to WESCO International Basic $ 4.87 $ 3.42 $ 2.30 Diluted $ 4.82 $ 3.38 $ 2.10 The computation of diluted earnings per share attributable to WESCO International excluded equity awards of approximately 1.6 million , 1.3 million and 1.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. These shares were excluded because their effect would have been antidilutive. Because of WESCO’s previous obligation to settle the par value of the 2029 Debentures in cash upon conversion, WESCO was required to include shares underlying the 2029 Debentures in its diluted weighted-average shares outstanding when the average stock price per share for the period exceeded the conversion price of the debentures. Only the number of shares that would have been issuable under the treasury stock method of accounting for share dilution were included, which was based upon the amount by which the average stock price exceeded the conversion price. The conversion price of the 2029 Debentures was $28.87 and the maximum amount of share dilution was limited to 11,951,932 shares. Since the 2029 Debentures were redeemed on September 15, 2016, there was no dilution from contingently convertible debentures for the years ended December 31, 2018 and 2017 . For the year ended December 31, 2016 , the effect of the 2029 Debentures on diluted earnings per share attributable to WESCO International was a decrease of $0.17 . In December 2014, the Company's Board of Directors (the "Board") authorized the repurchase of up to $300 million of the Company's common stock through December 31, 2017 (the "2014 Repurchase Authorization"). During the year ended December 31, 2017 , the Company repurchased 1,778,537 shares for $100.0 million . As of December 31, 2017 , WESCO had repurchased 4,247,113 shares of common stock for $250.0 million under the 2014 Repurchase Authorization. In December 2017, the Board authorized the repurchase of up to $300 million of the Company's common stock through December 31, 2020 (the "2017 Repurchase Authorization"). In October 2018, the Board approved an increase to the 2017 Repurchase Authorization from $300 million to $400 million . On September 6, 2018 and November 6, 2018 , the Company entered into accelerated stock repurchase agreements with a financial institution to repurchase additional shares of its common stock pursuant to its 2017 Repurchase Authorization. In exchange for up-front cash payments totaling $125.0 million , the Company received 2,003,446 shares. As of December 31, 2018 , the accelerated stock repurchase agreement entered into on November 6, 2018 had not yet settled between the counterparties. Upon settlement, the Company expects to receive additional shares. The total number of shares ultimately delivered under the accelerated stock repurchases described above are determined by the average of the volume-weighted-average prices of the Company's common stock for each exchange business day during the respective settlement valuation periods. WESCO funded the repurchases with available cash, and borrowings under its accounts receivable securitization and revolving credit facilities. For purposes of computing earnings per share, share repurchases have been reflected as a reduction to common shares outstanding on the respective delivery dates.

STOCK-BASED COMPENSATION STOCK-

STOCK-BASED COMPENSATION STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	14. STOCK-BASED COMPENSATION WESCO sponsors a stock-based compensation plan. The 1999 Long-Term Incentive Plan, as amended and restated (“LTIP”) was designed to be the successor plan to all prior plans. Any shares remaining reserved for future issuance under the prior plans are available for issuance under the LTIP. The LTIP is administered by the Compensation Committee of the Board. On May 31, 2017, the Company renewed and restated the LTIP, increasing the maximum number of shares of common stock that may be issued under the plan by 1.7 million shares to 3.4 million . Under the LTIP, the total number of shares of common stock authorized to be issued will be reduced by 1 share of common stock for every 1 share that is subject to a stock appreciation right granted, and 1.83 shares of common stock for every 1 share that is subject to an award other than a stock appreciation right granted on or after May 31, 2017. As of December 31, 2018 , 3.1 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 and performance-based awards with market conditions is determined using the Black-Scholes and Monte Carlo simulation models, respectively. The fair value of restricted stock units and performance-based awards with performance conditions is determined by the grant-date closing price of WESCO’s common stock. The forfeiture assumption is based on WESCO’s historical employee behavior that is reviewed on an annual basis. No dividends are assumed. For stock appreciation rights that are exercised and for restricted stock units and performance-based award that vest, shares are issued out of WESCO's outstanding common stock. Except for the performance-based awards, awards granted vest and become exercisable once criteria based on time is achieved. Performance-based awards vest based on market or performance conditions. In the event of a change in control, all awards vest immediately. Each award terminates on the tenth anniversary of its grant date unless terminated sooner under certain conditions. For awards granted in 2018, performance-based awards were based on two equally-weighted performance measures, which include the three-year average growth rate of the Company’s fully diluted earnings per share and the three-year cumulative return on net assets. From 2015 to 2017, the two equally-weighted performance-based award metrics were the three-year average growth rate of WESCO's net income and WESCO's total stockholder return in relation to the total stockholder return of a select group of peer companies over a three-year period. WESCO recognized $16.4 million , $14.8 million and $12.5 million of non-cash stock-based compensation expense, which is included in selling, general and administrative expenses, for the years ended December 31, 2018 , 2017 and 2016 , respectively. As of December 31, 2018 , there was $18.8 million of total unrecognized compensation expense related to non-vested stock-based compensation arrangements for all awards previously made of which approximately $11.7 million is expected to be recognized in 2019 , $6.3 million in 2020 and $0.8 million in 2021 . The total intrinsic value of awards exercised during the years ended December 31, 2018 , 2017 , and 2016 was $8.2 million , $17.2 million , and $13.0 million , respectively. The gross deferred tax benefit associated with the exercise of stock-based awards totaled $2.0 million , $6.4 million , and $4.9 million in 2018 , 2017 , and 2016 , respectively. The following table sets forth a summary of stock-settled stock appreciation rights and related information for the years presented: Year Ended December 31, 2018 2017 2016 Awards Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life Aggregate Intrinsic Value (In thousands) Awards Weighted-Average Exercise Price Awards Weighted-Average Exercise Price Beginning of year 2,238,607 $ 57.75 2,439,487 $ 52.62 2,567,021 $ 54.47 Granted 509,046 62.68 455,807 71.21 709,999 42.63 Exercised (192,700 ) 40.74 (495,181 ) 42.19 (526,818 ) 41.54 Canceled (203,320 ) 68.69 (161,506 ) 66.06 (310,715 ) 63.71 End of year 2,351,633 59.26 6.1 $ 6,514 2,238,607 57.75 2,439,487 52.62 Exercisable at end of year 1,453,932 $ 57.93 4.6 $ 5,623 1,331,580 $ 56.96 1,549,350 $ 53.35 The following table sets forth the weighted-average assumptions used to estimate the fair value of stock-settled stock appreciation rights granted during the years presented: Year Ended December 31, 2018 2017 2016 Stock-settled stock appreciation rights granted 509,046 455,807 709,999 Risk free interest rate 2.5% 1.9% 1.2% Expected life (in years) 5 5 5 Expected volatility 28% 29% 32% 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 $18.38 , $20.52 and $12.88 for the years ended December 31, 2018 , 2017 and 2016 , respectively. The following table sets forth a summary of time-based restricted stock units and related information for the years presented: Year Ended December 31, 2018 2017 2016 Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Unvested at beginning of year 290,054 $ 58.11 257,096 $ 57.47 175,411 $ 74.52 Granted 122,062 62.40 100,993 71.33 162,256 44.45 Vested (64,166 ) 67.91 (44,720 ) 84.57 (60,015 ) 72.41 Forfeited (20,152 ) 58.15 (23,315 ) 57.52 (20,556 ) 59.15 Unvested at end of year 327,798 $ 57.87 290,054 $ 58.11 257,096 $ 57.47 The following table sets forth a summary of performance-based awards and related information for the years presented: Year Ended December 31, 2018 2017 2016 Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Unvested at beginning of year 148,508 $ 60.23 149,320 $ 60.36 114,520 $ 76.48 Granted 44,144 62.80 39,978 76.63 91,768 47.00 Vested — — — — — — Forfeited (53,756 ) 64.67 (40,790 ) 76.77 (56,968 ) 71.25 Unvested at end of year 138,896 $ 59.33 148,508 $ 60.23 149,320 $ 60.36 The following table sets forth the assumptions used to estimate the fair value of performance shares granted during the years presented: Year ended December 31, 2018 2017 2016 Grant date share price $ 62.80 $ 71.67 $ 42.44 WESCO expected volatility n/a 29 % 26 % Peer group median volatility n/a 24 % 24 % Risk-free interest rate n/a 1.5 % 0.9 % Correlation of peer company returns n/a 114 % 122 % The unvested performance-based awards in the table above include 48,098 shares in which vesting of the ultimate number of shares is dependent upon WESCO's total stockholder return in relation to the total stockholder return of a select group of peer companies over a three-year period. These awards are accounted for as awards with market conditions; compensation cost is recognized over the service period, regardless of whether the market conditions are achieved and the awards ultimately vest. Vesting of the remaining 90,798 shares of performance-based awards in the table above is dependent upon the achievement of certain performance targets, including 48,098 that are dependent upon the three-year average growth rate of WESCO's net income, 21,350 that are dependent upon the three-year average growth rate of the Company's fully diluted earnings per share, and 21,350 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, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	16. COMMITMENTS AND CONTINGENCIES Future minimum rental payments required under operating leases, primarily for real property that have noncancelable lease terms in excess of one year as of December 31, 2018 , are as follows: Years ending December 31 (In thousands) 2019 $ 71,640 2020 59,594 2021 47,264 2022 34,490 2023 24,493 Thereafter 40,302 Rental expense for the years ended December 31, 2018 , 2017 and 2016 was $86.0 million , $82.0 million and $76.7 million , respectively. 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 a line of credit with a maximum borrowing capacity of approximately $6.7 million to support its working capital requirements and joint sales efforts with WESCO. Due to the nature of WESCO’s arrangement with WESTEC, WESCO has provided a standby letter of credit under its Revolving Credit Facility of up to $7.3 million as security for WESTEC’s line of credit. As of December 31, 2018 , WESTEC had an outstanding loan balance of $6.4 million . Management currently believes the estimated fair value of the noncontingent guarantee on the line of credit is nominal and therefore a liability has not been recorded as of December 31, 2018 .

SEGMENTS AND RELATED INFORMATIO

SEGMENTS AND RELATED INFORMATION	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
SEGMENTS AND RELATED INFORMATION	17. SEGMENTS AND RELATED INFORMATION WESCO distributes products and provides services through its four operating segments, which have been aggregated as one reportable segment. WESCO has approximately 220,000 unique product stock keeping units and markets more than 1,000,000 products for customers. There were no material amounts of sales or transfers among geographic areas and no material amounts of export sales. WESCO attributes revenues from external customers to individual countries on the basis of the point of sale. The following table sets forth information about WESCO by geographic area: Net Sales Year Ended December 31, Long-Lived Assets December 31, 2018 2017 2016 2018 2017 2016 (In thousands) United States $ 6,089,130 75 % $ 5,775,988 75 % $ 5,635,803 77 % $ 106,078 $ 95,851 $ 123,465 Other International (1) 2,087,471 25 % 1,903,033 25 % 1,700,214 23 % 54,800 60,594 65,182 Total $ 8,176,601 $ 7,679,021 $ 7,336,017 $ 160,878 $ 156,445 $ 188,647 (1) Other primarily includes Canada. The following table sets forth information about WESCO’s sales by product category: Year Ended December 31, 2018 2017 2016 (percentages based on total sales) General Supplies 40% 40% 40% Wire, Cable and Conduit 14% 15% 14% Communications and Security 16% 15% 15% Electrical Distribution and Controls 11% 10% 11% Lighting and Sustainability 11% 12% 12% Automation, Controls and Motors 8% 8% 8%

OTHER FINANCIAL INFORMATION

OTHER FINANCIAL INFORMATION	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information [Abstract]
OTHER FINANCIAL INFORMATION	18. CONDENSED CONSOLIDATING FINANCIAL INFORMATION WESCO Distribution has outstanding $500 million in aggregate principal amount of 2021 Notes and $350 million in aggregate principal amount of 2024 Notes. The 2021 Notes and 2024 Notes are unsecured senior obligations of WESCO Distribution and are fully and unconditionally guaranteed on a senior unsecured basis by WESCO International. Condensed consolidating financial information for WESCO International, WESCO Distribution and the non-guarantor subsidiaries is presented in the following tables. Condensed Consolidating Balance Sheet December 31, 2018 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Cash and cash equivalents $ — $ 35,931 $ 60,412 $ — $ 96,343 Trade accounts receivable, net — — 1,166,607 — 1,166,607 Inventories — 440,422 508,304 — 948,726 Prepaid expenses and other current assets 1,123 57,586 124,523 (9,268 ) 173,964 Total current assets 1,123 533,939 1,859,846 (9,268 ) 2,385,640 Intercompany receivables, net — — 2,403,704 (2,403,704 ) — Property, buildings and equipment, net — 63,506 97,372 — 160,878 Intangible assets, net — 2,131 313,885 — 316,016 Goodwill — 257,623 1,464,980 — 1,722,603 Investments in affiliates 3,182,469 5,137,783 (8,320,252 ) — Other assets — 2,905 16,994 19,899 Total assets $ 3,183,592 $ 5,997,887 $ 6,156,781 $ (10,733,224 ) $ 4,605,036 Accounts payable $ — $ 404,373 $ 389,975 $ — $ 794,348 Short-term debt — — 30,785 — 30,785 Other current liabilities — 86,600 159,481 (9,268 ) 236,813 Total current liabilities — 490,973 580,241 (9,268 ) 1,061,946 Intercompany payables, net 1,048,282 1,355,422 — (2,403,704 ) — Long-term debt — 842,093 325,218 — 1,167,311 Other noncurrent liabilities — 126,930 119,123 — 246,053 Total WESCO International stockholders’ equity 2,135,310 3,182,469 5,137,783 (8,320,252 ) 2,135,310 Noncontrolling interests — — (5,584 ) — (5,584 ) Total liabilities and stockholders’ equity $ 3,183,592 $ 5,997,887 $ 6,156,781 $ (10,733,224 ) $ 4,605,036 Condensed Consolidating Balance Sheet December 31, 2017 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Cash and cash equivalents $ — $ 50,602 $ 67,351 $ — $ 117,953 Trade accounts receivable, net — — 1,170,080 — 1,170,080 Inventories — 430,092 526,056 — 956,148 Prepaid expenses and other current assets 4,730 42,547 152,531 (35,140 ) 164,668 Total current assets 4,730 523,241 1,916,018 (35,140 ) 2,408,849 Intercompany receivables, net — — 2,189,136 (2,189,136 ) — Property, buildings and equipment, net — 50,198 106,247 — 156,445 Intangible assets, net — 2,770 364,334 — 367,104 Goodwill — 257,623 1,514,254 — 1,771,877 Investments in affiliates 3,058,613 5,023,826 — (8,082,439 ) — Other assets — 2,778 28,415 — 31,193 Total assets $ 3,063,343 $ 5,860,436 $ 6,118,404 $ (10,306,715 ) $ 4,735,468 Accounts payable $ — $ 417,690 $ 381,830 $ — $ 799,520 Short-term debt — — 34,075 — 34,075 Other current liabilities — 80,039 162,475 (35,140 ) 207,374 Total current liabilities — 497,729 578,380 (35,140 ) 1,040,969 Intercompany payables, net 939,784 1,249,352 — (2,189,136 ) — Long-term debt — 934,033 379,228 — 1,313,261 Other noncurrent liabilities 3,820 120,709 140,566 — 265,095 Total WESCO International stockholders’ equity 2,119,739 3,058,613 5,023,826 (8,082,439 ) 2,119,739 Noncontrolling interests — — (3,596 ) — (3,596 ) Total liabilities and stockholders’ equity $ 3,063,343 $ 5,860,436 $ 6,118,404 $ (10,306,715 ) $ 4,735,468 Condensed Consolidating Statement of Income and Comprehensive Income Year ended December 31, 2018 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net sales $ — $ 3,572,406 $ 4,757,321 $ (153,126 ) $ 8,176,601 Cost of goods sold (excluding depreciation and — 2,890,490 3,871,856 (153,126 ) 6,609,220 amortization) Selling, general and administrative expenses — 590,009 561,935 — 1,151,944 Depreciation and amortization — 18,334 44,663 — 62,997 Results of affiliates’ operations 225,355 209,802 — (435,157 ) — Net interest and other — 54,178 17,237 — 71,415 Provision for income taxes — 3,842 51,828 — 55,670 Net income 225,355 225,355 209,802 (435,157 ) 225,355 Less: Net loss attributable to noncontrolling interests — — (1,988 ) — (1,988 ) Net income attributable to WESCO International $ 225,355 $ 225,355 $ 211,790 $ (435,157 ) $ 227,343 Other comprehensive income (loss): Foreign currency translation adjustments (99,643 ) (99,643 ) (99,643 ) 199,286 (99,643 ) Post retirement benefit plan adjustments, net of tax 3,798 3,798 3,798 (7,596 ) 3,798 Comprehensive income attributable to WESCO International $ 129,510 $ 129,510 $ 115,945 $ (243,467 ) $ 131,498 Condensed Consolidating Statement of Income and Comprehensive Income Year ended December 31, 2017 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net sales $ — $ 3,370,088 $ 4,441,655 $ (132,722 ) $ 7,679,021 Cost of goods sold (excluding depreciation and — 2,714,511 3,612,577 (132,722 ) 6,194,366 amortization) Selling, general and administrative expenses — 555,503 546,095 — 1,101,598 Depreciation and amortization — 18,442 45,575 — 64,017 Results of affiliates’ operations 160,587 168,782 — (329,369 ) — Net interest and other — 94,313 (27,713 ) — 66,600 Provision for income taxes (2,546 ) (4,486 ) 96,339 — 89,307 Net income 163,133 160,587 168,782 (329,369 ) 163,133 Less: Net loss attributable to noncontrolling interests — — (327 ) — (327 ) Net income attributable to WESCO International $ 163,133 $ 160,587 $ 169,109 $ (329,369 ) $ 163,460 Other comprehensive income (loss): Foreign currency translation adjustments 85,762 85,762 85,762 (171,524 ) 85,762 Post retirement benefit plan adjustments, net of tax (6,381 ) (6,381 ) (6,381 ) 12,762 (6,381 ) Comprehensive income attributable to WESCO International $ 242,514 $ 239,968 $ 248,490 $ (488,131 ) $ 242,841 Condensed Consolidating Statement of Income and Comprehensive Income Year ended December 31, 2016 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net sales $ — $ 3,306,265 $ 4,134,508 $ (104,756 ) $ 7,336,017 Cost of goods sold (excluding depreciation and — 2,651,409 3,341,161 (104,756 ) 5,887,814 amortization) Selling, general and administrative expenses 61 477,437 573,301 — 1,050,799 Depreciation and amortization — 20,226 46,632 — 66,858 Results of affiliates’ operations 240,571 155,814 — (396,385 ) — Net interest and other 17,555 87,824 (30,317 ) — 75,062 Loss on debt redemption 123,933 — — — 123,933 Provision for income taxes (2,098 ) 8,263 24,266 — 30,431 Net income $ 101,120 $ 216,920 $ 179,465 $ (396,385 ) $ 101,120 Less: Net loss attributable to noncontrolling interests — — (468 ) — (468 ) Net income attributable to WESCO International $ 101,120 $ 216,920 $ 179,933 $ (396,385 ) $ 101,588 Other comprehensive income (loss): Foreign currency translation adjustments 38,275 38,275 38,275 (76,550 ) 38,275 Post retirement benefit plan adjustments, net of tax (2,485 ) (2,485 ) (2,485 ) 4,970 (2,485 ) Comprehensive income attributable to WESCO International $ 136,910 $ 252,710 $ 215,723 $ (467,965 ) $ 137,378 Reclassification As described in Note 13, the Company reclassified a net benefit of $1.8 million and $1.5 million , respectively, from selling, general and administrative expenses to net interest and other in the previously reported Condensed Consolidated Statement of Income and Comprehensive Income of the non-guarantor subsidiaries for the years ended December 31, 2017 and 2016 , respectively. Condensed Consolidating Statement of Cash Flows Year ended December 31, 2018 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net cash provided by operating activities $ 18,672 $ 153,467 $ 124,582 $ — $ 296,721 Investing activities: Capital expenditures — (17,573 ) (18,637 ) — (36,210 ) Proceeds from sale of assets — — 12,461 — 12,461 Dividends received from subsidiaries 347,531 (347,531 ) — Advances to subsidiaries and other — (406,028 ) 196,219 199,416 (10,393 ) Net cash (used in) provided by investing activities — (76,070 ) 190,043 (148,115 ) (34,142 ) Financing activities: Proceeds from issuance of debt 108,497 339,606 1,086,673 (199,416 ) 1,335,360 Repayments of debt — (410,606 ) (1,051,611 ) — (1,462,217 ) Equity activities (127,169 ) — — — (127,169 ) Dividends paid by subsidiaries (347,531 ) 347,531 — Other — (21,068 ) — — (21,068 ) Net cash used in financing activities (18,672 ) (92,068 ) (312,469 ) 148,115 (275,094 ) Effect of exchange rate changes on cash and cash equivalents (9,095 ) — (9,095 ) Net change in cash and cash equivalents — (14,671 ) (6,939 ) — (21,610 ) Cash and cash equivalents at the beginning of period — 50,602 67,351 — 117,953 Cash and cash equivalents at the end of period $ — $ 35,931 $ 60,412 $ — $ 96,343 Condensed Consolidating Statement of Cash Flows Year ended December 31, 2017 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net cash (used in) provided by operating activities $ (36,575 ) $ 101,826 $ 83,871 $ — $ 149,122 Investing activities: Capital expenditures — (13,215 ) (8,292 ) — (21,507 ) Proceeds from sale of assets — — 6,766 — 6,766 Dividends received from subsidiaries — 307,784 — (307,784 ) — Advances to subsidiaries and other — (383,686 ) 26,912 366,220 9,446 Net cash (used in) provided by investing activities — (89,117 ) 25,386 58,436 (5,295 ) Financing activities: Proceeds from issuance of debt 143,367 775,926 1,144,848 (383,686 ) 1,680,455 Repayments of debt — (785,392 ) (952,740 ) 17,466 (1,720,666 ) Equity activities (106,792 ) — — — (106,792 ) Dividends paid by subsidiaries — — (307,784 ) 307,784 — Other — 5,807 — — 5,807 Net cash provided by (used in) financing activities 36,575 (3,659 ) (115,676 ) (58,436 ) (141,196 ) Effect of exchange rate changes on cash and cash equivalents — — 5,191 — 5,191 Net change in cash and cash equivalents — 9,050 (1,228 ) — 7,822 Cash and cash equivalents at the beginning of period — 41,552 68,579 — 110,131 Cash and cash equivalents at the end of period $ — $ 50,602 $ 67,351 $ — $ 117,953 Condensed Consolidating Statement of Cash Flows Year ended December 31, 2016 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net cash provided by (used in) operating activities $ 95,388 $ (243,476 ) $ 448,323 $ — $ 300,235 Investing activities: Capital expenditures — (12,482 ) (5,475 ) — (17,957 ) Acquisition payments, net of cash acquired — (50,890 ) — — (50,890 ) Proceeds from sale of assets — — 8,361 — 8,361 Dividends received from subsidiaries — 82,912 — (82,912 ) — Advances to subsidiaries and other — (297,259 ) (337,344 ) 624,603 (10,000 ) Net cash used in investing activities — (277,719 ) (334,458 ) 541,691 (70,486 ) Financing activities: Proceeds from issuance of debt 252,246 1,566,864 672,345 (297,259 ) 2,194,196 Repayments of debt (344,804 ) (1,030,520 ) (752,401 ) (327,344 ) (2,455,069 ) Equity activities (2,830 ) — — — (2,830 ) Dividends paid by subsidiaries — — (82,912 ) 82,912 — Other — (12,560 ) — — (12,560 ) Net cash (used in) provided by financing activities (95,388 ) 523,784 (162,968 ) (541,691 ) (276,263 ) Effect of exchange rate changes on cash and cash equivalents — — (3,634 ) — (3,634 ) Net change in cash and cash equivalents — 2,589 (52,737 ) — (50,148 ) Cash and cash equivalents at the beginning of period — 38,963 121,316 — 160,279 Cash and cash equivalents at the end of period $ — $ 41,552 $ 68,579 $ — $ 110,131

SELECTED QUARTERLY FINANCIAL DA

SELECTED QUARTERLY FINANCIAL DATA	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
SELECTED QUARTERLY FINANCIAL DATA	19. SELECTED QUARTERLY FINANCIAL DATA (unaudited) The following table sets forth selected quarterly financial data for the years ended December 31, 2018 and 2017 : First Quarter Second Quarter Third Quarter Fourth Quarter 2018 Net Sales $ 1,993,915 $ 2,103,994 $ 2,067,245 $ 2,011,447 Cost of goods sold (excluding depreciation and amortization) 1,613,966 1,704,100 1,670,037 1,621,117 Income from operations 73,241 91,183 97,517 90,499 Income before income taxes 53,458 73,442 80,467 73,658 Net income 42,971 57,673 66,645 58,066 Net income attributable to WESCO International 44,421 57,940 66,849 58,133 Basic earnings per share attributable to WESCO International (2) 0.94 1.23 1.42 1.27 Diluted earnings per share attributable to WESCO International (3) 0.93 1.22 1.41 1.26 2017 Net Sales $ 1,772,591 $ 1,909,624 $ 2,000,159 $ 1,996,647 Cost of goods sold (excluding depreciation and amortization) 1,422,573 1,543,510 1,614,814 1,613,469 Income from operations 67,089 83,105 89,250 81,446 Income before income taxes 50,368 66,289 71,939 63,844 Net income (1) 37,800 49,535 53,576 22,222 Net income attributable to WESCO International (1) 37,729 49,510 53,675 22,546 Basic earnings per share attributable to WESCO International (1) (2) 0.77 1.03 1.13 0.48 Diluted earnings per share attributable to WESCO International (1) (3) 0.76 1.02 1.12 0.47 (1) As described in Note 11, net income and net income attributable to WESCO International include provisional discrete income tax expense of $26.4 million resulting from the application of the TCJA, which affected basic and diluted earnings per share attributable to WESCO International in the fourth quarter of 2017. (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 EVENT

SUBSEQUENT EVENT	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	20. SUBSEQUENT EVENTS On January 16, 2019, WESCO issued a press release announcing that its WESCO Services, LLC subsidiary entered into a definitive agreement to acquire certain assets of Sylvania Lighting Solutions from OSRAM Sylvania. The transaction is expected to close in March 2019.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Schedule II—Valuation and Qualifying Accounts Balance at Beginning Charged to Charged to Other Balance at of Period Expense Accounts (1) Deductions (2) End of Period Allowance for doubtful accounts (In thousands) Year ended December 31, 2018 $ 21,313 10,854 — (7,699 ) $ 24,468 Year ended December 31, 2017 22,007 8,466 — (9,160 ) 21,313 Year ended December 31, 2016 22,587 5,888 21 (6,489 ) 22,007 _________________________ (1) Represents allowance for doubtful accounts in connection with certain acquisitions and divestitures. (2) Includes a reduction in the allowance for doubtful accounts due to write-off of accounts receivable.

REVENUE (Notes)

REVENUE (Notes)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Policy Text Block]	3. REVENUE WESCO distributes products and provides services to customers globally within the following end markets: (1) industrial, (2) construction, (3) utility, and (4) commercial, institutional and government. Revenue is measured as the amount of consideration WESCO expects to receive in exchange for transferring goods or providing services. The following tables disaggregate WESCO’s net sales by end market and geography: Year Ended December 31, (In thousands) 2018 2017 2016 Industrial $ 2,983,062 $ 2,852,357 $ 2,644,442 Construction 2,684,844 2,546,261 2,482,624 Utility 1,303,697 1,181,704 1,158,651 Commercial, Institutional and Government 1,204,998 1,098,699 1,050,300 Total by end market $ 8,176,601 $ 7,679,021 $ 7,336,017 Year Ended December 31, (In thousands) 2018 2017 2016 United States $ 6,089,130 $ 5,775,988 $ 5,635,803 Other (1) 2,087,471 1,903,033 1,700,214 Total by geography $ 8,176,601 $ 7,679,021 $ 7,336,017 (1) Other primarily includes net sales originating in Canada. The amount of revenue recognized for integrated supply services totaled $23.3 million , $26.2 million , and $27.1 million in 2018 , 2017 and 2016 , respectively. 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, 2018 and 2017 , $11.8 million and $15.5 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, 2018 , 2017 and 2016 by approximately $107.4 million , $91.1 million and $79.9 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 $74.1 million , $61.8 million and $57.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.

FAIR VALUE (Notes)

FAIR VALUE (Notes)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Disclosures [Text Block]	4. FAIR VALUE OF FINANCIAL INSTRUMENTS The Company’s financial instruments consist of cash and cash equivalents, accounts receivable, accounts payable, bank overdrafts, and outstanding indebtedness. The Company uses a market approach to determine the fair value of its debt instruments, utilizing quoted prices in active markets, interest rates and other relevant information generated by market transactions involving similar instruments. Therefore, the inputs used to measure the fair value of the Company's debt instruments are classified as Level 2 within the fair value hierarchy. The reported carrying amounts of WESCO's financial instruments approximated their fair values as of December 31, 2018 and 2017 .

Net Interest and Other (Notes)

Net Interest and Other (Notes)	12 Months Ended
	Dec. 31, 2018
Income Statement [Abstract]
Other Nonoperating Income and Expense [Text Block]	15. NET INTEREST AND OTHER Net interest and other includes interest expense, interest income, amortization of debt discount and debt issuance costs, the non-service cost components of net periodic benefit cost, and foreign exchange gains and losses from the remeasurement of certain financial instruments. For the year ended December 31, 2018 , a foreign exchange loss of $2.8 million from the remeasurement of certain financial instruments was reported as a component of net interest and other. Foreign exchange gains and losses were not material for the years ended December 31, 2017 and 2016 .

ACCOUNTING POLICIES (Policies)

ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Consolidation	Basis of Consolidation The consolidated financial statements include the accounts of WESCO International and all of its subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Although these estimates are based on management’s best knowledge of current events and actions WESCO may undertake in the future, actual results may ultimately differ from the estimates.
Revenue Recognition	Revenue Recognition WESCO’s revenue arrangements generally consist of single performance obligations to transfer a promised good or service, or a combination of goods and services. Revenue is recognized when control has transferred to the customer, which is generally when the product has shipped from a WESCO facility or directly from a supplier. For products that ship directly from suppliers to customers, WESCO acts as the principal in the transaction and recognizes revenue on a gross basis. Revenue for integrated supply services is recognized over time based on hours incurred as the transfer of control occurs as the services are being performed. WESCO generally satisfies its performance obligations within a year or less. WESCO generally does not have significant financing terms associated with its contracts; payments are normally received within 60 days. There are generally no significant costs associated with obtaining customer contracts. WESCO generally passes through warranties offered by manufacturers or suppliers to its customers. Sales taxes (and value added taxes in foreign jurisdictions) collected from customers and remitted to governmental authorities are excluded from net sales.
Supplier Volume Rebates	Supplier Volume Rebates WESCO receives volume rebates from certain suppliers based on contractual arrangements with such suppliers. Volume rebates are included within other accounts receivable in the Consolidated Balance Sheets, and represent the estimated amounts due to WESCO based on forecasted purchases and the rebate provisions of the various supplier contracts. The corresponding rebate income is recorded as a reduction to cost of goods sold. Receivables under the supplier rebate program were $73.5 million at December 31, 2018 and $72.7 million at December 31, 2017 . In 2018 , 2017 and 2016 , the supplier volume rebate as a percentage of net sales was 1.3% .
Shipping and Handling Costs and Fees	Shipping and handling costs are recognized in net sales when they are billed to the customer. These costs are recognized as a component of selling, general and administrative expenses when WESCO does not bill the customer. WESCO has elected to recognize shipping and handling costs as a fulfillment cost. Shipping and handling costs recorded as a component of selling, general and administrative expenses totaled $74.1 million , $61.8 million and $57.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.
Cash Equivalents	Cash Equivalents Cash equivalents are defined as highly liquid investments with original maturities of 90 days or less when purchased.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts WESCO maintains allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments. WESCO has a systematic procedure using historical data and reasonable assumptions of collectability made at the local branch level and on a consolidated corporate basis to estimate allowances for doubtful accounts. If the financial condition of WESCO’s customers were to deteriorate, resulting in an impairment of their ability to make payments, additional allowances may be required. The allowance for doubtful accounts was $24.5 million at December 31, 2018 and $21.3 million at December 31, 2017 . The total amount recorded as selling, general and administrative expense related to bad debts was $10.9 million , $8.5 million and $5.9 million for 2018 , 2017 and 2016 , respectively.
Inventories	Inventories Inventories primarily consist of merchandise purchased for resale and are stated at the lower of cost and net realizable value. Cost is determined principally under the average cost method. WESCO makes provisions for obsolete or slow-moving inventories as necessary to reflect reductions in value. WESCO writes down its inventories to net realizable value based on internal factors derived from historical analysis of actual losses. WESCO uses past data to identify items in excess of 36 months supply relative to demand or movement. WESCO then analyzes the ultimate disposition of identified excess inventories as they are sold, returned to supplier, or scrapped. This historical item-by-item analysis allows WESCO to develop an estimate of the likelihood that an item identified as being in excess supply ultimately becomes obsolete. WESCO applies the estimate to inventories currently in excess of 36 months supply, and reduces the carrying value of its inventories by the derived amount. Reserves for excess and obsolete inventories were $27.6 million and $28.6 million at December 31, 2018 and 2017 , respectively. The total expense related to excess and obsolete inventories, included in cost of goods sold, was $9.7 million , $8.8 million and $7.3 million for 2018 , 2017 and 2016 , respectively. WESCO absorbs into the cost of inventories certain overhead expenses such as purchasing, receiving and storage and at December 31, 2018 and 2017 , $69.2 million and $70.7 million , respectively, of these costs were included in ending inventories.
Property, Buildings and Equipment	Property, Buildings and Equipment Property, buildings and equipment are recorded at cost. Depreciation expense is determined using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over either their respective lease terms or their estimated lives, whichever is shorter. Estimated useful lives range from five to forty years for buildings and leasehold improvements and three to ten years for furniture, fixtures and equipment. Capitalized computer software costs are amortized using the straight-line method over the estimated useful life, typically three to five years , and are reported at the lower of unamortized cost or net realizable value. Expenditures for new facilities and improvements that extend the useful life of an asset are capitalized. Ordinary repairs and maintenance are expensed as incurred. When property is retired or otherwise disposed of, the cost and the related accumulated depreciation are removed from the accounts and any resulting gains or losses are recorded and reported as selling, general and administrative expenses. Of WESCO’s $160.9 million net book value of property, buildings and equipment as of December 31, 2018 , $88.3 million consists of land, buildings and leasehold improvements that are geographically dispersed among WESCO’s 500 branches and 10 distribution centers, mitigating the risk of impairment. WESCO assesses its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of any such assets may not be fully recoverable. Changes in circumstances include technological advances, changes in the business model, capital structure, economic conditions or operating performance. The evaluation is based upon, among other things, utilization, serviceability and assumptions about the estimated future undiscounted cash flows that these assets are expected to generate. When the sum of the undiscounted cash flows is less than the carrying value of the asset or asset group, an impairment loss is recognized to the extent that carrying value exceeds fair value. Management applies its best judgment when performing these evaluations.
Goodwill and Intangible Assets	Goodwill and Indefinite-Lived Intangible Assets Goodwill and indefinite-lived intangible assets are tested for impairment annually during the fourth quarter using information available at the end of September, or more frequently if triggering events occur, indicating that their carrying value may not be recoverable. WESCO tests for goodwill impairment on a reporting unit level and the evaluation involves comparing the fair value of each reporting unit to its carrying value. The fair values of the reporting units are determined using a combination of a discounted cash flow analysis and market multiples. Assumptions used for these fair value techniques are based on a combination of historical results, current forecasts, market data and recent economic events. WESCO evaluates the recoverability of indefinite-lived intangible assets using the relief-from-royalty method based on projected financial information. At December 31, 2018 and 2017 , respectively, goodwill and indefinite-lived trademarks totaled $1.8 billion and $1.9 billion . We performed our annual impairment tests of goodwill and indefinite-lived intangible assets during the fourth quarter. A possible indicator of goodwill impairment is the relationship of a company’s market capitalization to its book value. As of December 31, 2018 , our market capitalization exceeded our book value and the fair values of our reporting units exceeded their carrying values. Accordingly, there were no impairment losses identified as a result of our annual test. The determination of fair value involves significant management judgment and management applies its best judgment when assessing the reasonableness of financial projections. Fair values are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill and indefinite-lived intangible impairment tests will prove to be an accurate prediction of future results.
Definite Lived Intangible Assets	Definite Lived Intangible Assets Definite lived intangible assets are amortized over 2 to 20 years. A portion of definite lived intangible assets related to certain customer relationships are amortized using an accelerated method whereas all other definite lived intangible assets subject to amortization use a straight-line method. In either case, the amortization method reflects the pattern in which the economic benefits of the respective assets are consumed or otherwise used. Definite lived intangible assets are tested for impairment if events or circumstances occur indicating that the respective asset might be impaired.
Insurance Programs	Insurance Programs WESCO uses commercial insurance for auto, workers’ compensation, casualty and health claims, and information technology as a risk-reduction strategy to minimize catastrophic losses. The Company’s strategy involves large deductible policies where WESCO must pay all costs up to the deductible amount. WESCO estimates the reserve for these programs based on historical incident rates and costs. The assumptions included in developing this accrual include the period of time between the incurrence and payment of a claim. The total liability related to the insurance programs was $13.1 million and $13.9 million at December 31, 2018 and 2017 , respectively.
Income Taxes	Income Taxes WESCO accounts for income taxes under the asset and liability method, which requires the recognition of deferred income taxes for events that have future tax consequences. Under this method, deferred income taxes are recognized (using enacted tax laws and rates) based on the future income tax effects of differences in the carrying amounts of assets and liabilities for financial reporting and tax purposes. The effect of a tax rate change on deferred tax assets and liabilities is recognized in income in the period of change. WESCO recognizes deferred tax assets at amounts that are expected to be realized. To make such determination, management evaluates all positive and negative evidence, including but not limited to, prior, current and future taxable income, tax planning strategies and future reversals of existing temporary differences. A valuation allowance is recognized if it is “more-likely-than-not” that some or all of a deferred tax asset will not be realized. WESCO regularly assesses the realizability of deferred tax assets. WESCO accounts for uncertainty in income taxes using a "more-likely-than-not" recognition threshold. Due to the subjectivity inherent in the evaluation of uncertain tax positions, the tax benefit ultimately recognized may materially differ from the estimate. WESCO recognizes interest and penalties related to uncertain tax benefits as part of interest expense and income tax expense, respectively. The Tax Cuts and Jobs Act of 2017 (the “TCJA”) imposed a one-time tax on the deemed repatriation of undistributed foreign earnings (the "transition tax"). Except for a portion of the previously taxed foreign earnings that have been repatriated, WESCO continues to assert that the remaining undistributed earnings of its foreign subsidiaries, the majority of which were subject to the transition tax, are indefinitely reinvested. WESCO believes it is able to maintain a sufficient level of liquidity for its domestic operations and commitments without repatriating cash held by these foreign subsidiaries. Upon any future repatriation, additional income taxes may be incurred; however, it is not practicable to determine the amount at this time. The provisions of the TCJA also introduced U.S. taxation on certain global intangible low-taxed income ("GILTI"). WESCO has elected to account for GILTI tax as a component of income tax expense. Future adjustments (if any) resulting from additional regulatory guidance regarding the accounting for the income tax effects of TCJA will be recognized as discrete income tax expense or benefit in the period in which guidance is issued.
Foreign Currency	Foreign Currency The local currency is the functional currency for the majority of WESCO’s operations outside the United States. Assets and liabilities of these operations are translated to U.S. dollars at the exchange rate in effect at the end of each period. Income statement accounts are translated at an exchange rate that approximates the average for the period. Translation adjustments arising from the use of differing exchange rates from period to period are included as a component of other comprehensive income (loss) within stockholders’ equity. Gains and losses from foreign currency transactions are included in net income for the period.
Defined Benefit Pension Plan	Defined Benefit Pension Plan Liabilities and expenses for pension benefits are determined using actuarial methodologies and incorporate significant assumptions, including the interest rate used to discount the future estimated cash flows, the expected long-term rate of return on plan assets, and several assumptions relating to the employee workforce (salary increases, retirement age, and mortality).
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company measures the fair value of financial assets and liabilities according to a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value and requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of the fair value hierarchy are as follows: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible at the measurement date; Level 2 inputs include inputs other than Level 1 that are observable, either directly or indirectly, and Level 3 inputs are unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to measurements involving significant unobservable inputs (Level 3).
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Adopted Accounting Pronouncements Effective January 1, 2018, WESCO adopted ASU 2014-09, Revenue from Contracts with Customers , and all the related amendments (“Topic 606”) using the modified retrospective approach to all open contracts (see Note 3 below). There was no impact to WESCO’s previously reported consolidated financial statements and WESCO does not expect the adoption of Topic 606 to have a material impact on its revenue and results of operations on an ongoing basis. In August 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (a consensus of the Emerging Issues Task Force) . This ASU provided guidance on eight specific cash flow issues where there was diversity in practice. The Company adopted this ASU in the first quarter of 2018. The adoption of this guidance did not have an impact on the consolidated financial statements and notes presented herein. In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, which eliminates Step 2 of the goodwill impairment test. Under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit to its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity should apply the amendments in this ASU on a prospective basis. This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Management adopted this ASU in the fourth quarter of 2018 when the Company performed its annual impairment tests. The adoption of this accounting standard did not have an impact on the consolidated financial statements and notes presented herein. In March 2017, the FASB issued ASU 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . This ASU requires that an employer disaggregate the service cost from the other components of net benefit cost. The Company adopted this guidance on a retrospective basis in the first quarter of 2018. See Note 13 for a description of the impact of this accounting standard on the Consolidated Statements of Income and Comprehensive Income presented herein. The adoption of this guidance did not have an impact on the Company's Consolidated Balance Sheets and the Consolidated Statements of Cash Flows presented herein. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting. This ASU clarifies when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the change in terms or conditions. The Company adopted this ASU in the first quarter of 2018. The adoption of this guidance did not have an impact on the consolidated financial statements presented and notes herein. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases , a comprehensive new standard that amends various aspects of existing accounting guidance for leases, including the recognition of a right-of-use asset and a lease liability in the balance sheet and disclosing key information about leasing arrangements. This ASU is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. During 2018, the FASB issued additional ASUs that address implementation issues and correct or improve certain aspects of the new accounting guidance for leases, including ASU 2018-10, Codification Improvements to Topic 842, Leases and ASU 2018-11, Leases (Topic 842): Targeted Improvements. These ASUs do not change the core principles in the leasing standard outlined above. The amendments in ASU 2018-11 provide an optional transition method that allows entities to initially apply the new lease standard at the adoption date. Consequently, an entity’s reporting for the comparative periods will continue to be in accordance with current lease accounting guidance. During 2018, management established a cross-functional team to evaluate and implement the new standard. The team selected a third-party software solution to facilitate the accounting and financial reporting requirements of the new lease standard. Lease data elements have been gathered and migrated to the software solution. The new standard will be adopted in the first quarter of 2019. The Company expects to use the optional transition method and elect the package of practical expedients permitted under the transition guidance. The Company also expects to elect the practical expedient related to lease and nonlease components. The Company anticipates recording right-of-use assets and lease liabilities of $200 million to $250 million in the Consolidated Balance Sheet as of January 1, 2019, most of which will relate to real estate. The Company does not expect the adoption to have a material impact on the Consolidated Statement of Income and Comprehensive Income (Loss) or Consolidated Statement of Cash Flow. The Company is currently updating business processes and internal controls to meet the standard’s new accounting, reporting and disclosure requirements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which introduces new guidance for the accounting for credit losses on certain financial instruments. The amendments in this ASU are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement , which amends the disclosure requirements for recurring and nonrecurring fair value measurements by removing, modifying and adding certain disclosures. The amendments in this ASU are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. In August 2018, the FASB issued ASU 2018-14, Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans , which amends the disclosure requirements for all employers that sponsor defined benefit pension and other post retirement plans by removing and adding certain disclosures. The amendments in this ASU are effective for fiscal years ending after December 15, 2020. Early adoption is permitted. Management does not expect the adoption of this accounting standard to have a material impact on its consolidated financial statements and notes thereto. 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.
Accounting Changes and Error Corrections [Text Block]	Correction of Prior Period Management determined that the deferred tax asset related to stock-based compensation was overstated by $5.7 million due to equity awards that had expired subsequent to the requisite service period in years 2016 and prior. In accordance with Staff Accounting Bulletin (“SAB”) No. 99, Materiality , and SAB No. 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements , management concluded that this misstatement is not material to the Company's previously issued annual and interim financial statements, and the correction of this item in the year ended December 31, 2018 is not material to the 2018 consolidated financial statements presented herein. The Company recorded an adjustment to decrease deferred income taxes and additional capital in the Consolidated Balance Sheet at December 31, 2018 .
Reclassification, Policy [Policy Text Block]	Reclassifications Effective January 1, 2018, WESCO adopted Accounting Standards Update (ASU) 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . The adoption of this ASU, as described below and in Note 13, resulted in the reclassification of amounts reported in the Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2017 and 2016 . The Consolidated Balance Sheet as of December 31, 2017 and the Consolidated Statements of Cash Flows for the years ended December 31, 2017 and 2016 include certain reclassifications to previously reported amounts to conform to the current period's presentation.

COMMITMENTS AND CONTINGENCIES G

COMMITMENTS AND CONTINGENCIES Guarantee (Policies)	12 Months Ended
	Dec. 31, 2018
Guarantees and Product Warranties [Abstract]
Guarantees [Text Block]	In an effort to expand the Company's footprint in the Middle East, WESCO has been doing business since 2009 with WESTEC Supplies General Trading (“WESTEC”), an industrial equipment supplier headquartered in the United Arab Emirates. WESTEC has a line of credit with a maximum borrowing capacity of approximately $6.7 million to support its working capital requirements and joint sales efforts with WESCO. Due to the nature of WESCO’s arrangement with WESTEC, WESCO has provided a standby letter of credit under its Revolving Credit Facility of up to $7.3 million as security for WESTEC’s line of credit. As of December 31, 2018 , WESTEC had an outstanding loan balance of $6.4 million . Management currently believes the estimated fair value of the noncontingent guarantee on the line of credit is nominal and therefore a liability has not been recorded as of December 31, 2018 .

REVENUE Revenue Reductions (Pol

REVENUE Revenue Reductions (Policies)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition, Revenue Reductions [Policy Text Block]	WESCO’s revenues are adjusted for variable consideration, which includes customer volume rebates, returns, and discounts. WESCO measures variable consideration by estimating expected outcomes using analysis and inputs based upon historical data, as well as current and forecasted information. Variable consideration is reviewed by management on a monthly basis and revenue is adjusted accordingly. Variable consideration reduced revenue for the years ended December 31, 2018 , 2017 and 2016 by approximately $107.4 million , $91.1 million and $79.9 million , respectively.

REVENUE Shipping and Handling (

REVENUE Shipping and Handling (Policies)	12 Months Ended
	Dec. 31, 2018
Income Statement [Abstract]
Shipping and Handling Cost, Policy [Policy Text Block]	Shipping and handling costs are recognized in net sales when they are billed to the customer. These costs are recognized as a component of selling, general and administrative expenses when WESCO does not bill the customer. WESCO has elected to recognize shipping and handling costs as a fulfillment cost. Shipping and handling costs recorded as a component of selling, general and administrative expenses totaled $74.1 million , $61.8 million and $57.9 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 (In thousands) Beginning balance January 1 $ 1,771,877 $ 1,730,950 Foreign currency exchange rate changes (49,274 ) 40,927 Ending balance December 31 $ 1,722,603 $ 1,771,877
Schedule of Intangible Assets by Major Class	The components of intangible assets are as follows: December 31, 2018 December 31, 2017 Life Gross Carrying Amount (1) Accumulated Amortization (1) Net Carrying Amount Gross Carrying Amount (1) Accumulated Amortization (1) Net Carrying Amount (In thousands) Intangible assets: Trademarks Indefinite $ 96,260 $ — $ 96,260 $ 100,249 $ — $ 100,249 Trademarks 4-15 25,185 (7,585 ) 17,600 25,118 (5,516 ) 19,602 Non-compete agreements 2-7 196 (141 ) 55 196 (102 ) 94 Customer relationships 2-20 358,620 (180,395 ) 178,225 377,270 (161,711 ) 215,559 Distribution agreements 10-19 36,984 (22,562 ) 14,422 39,515 (22,200 ) 17,315 Patents 10 48,310 (38,856 ) 9,454 48,310 (34,025 ) 14,285 $ 565,555 $ (249,539 ) $ 316,016 $ 590,658 $ (223,554 ) $ 367,104 (1) Excludes the original cost and related accumulated amortization of fully-amortized intangible assets.
Schedule of Expected Amortization Expense	The following table sets forth the estimated amortization expense for intangible assets for the next five years and thereafter: For the year ending December 31, (In thousands) 2019 $ 35,269 2020 33,417 2021 25,809 2022 23,431 2023 22,877 Thereafter 78,953

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Business Acquisition [Line Items]
Schedule of Business Acquisitions, by Acquisition	The following table sets forth the consideration paid for acquisitions: Year Ended December 31, 2016 (In thousands) Fair value of assets acquired $ 76,980 Fair value of liabilities assumed 25,058 Cash paid for acquisitions $ 51,922 Supplemental cash flow disclosure related to acquisitions: Cash paid for acquisitions $ 51,922 Less: cash acquired (1,032 ) Cash paid for acquisitions, net of cash acquired $ 50,890

PROPERTY, BUILDINGS AND EQUIP_2

PROPERTY, BUILDINGS AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 (In thousands) Buildings and leasehold improvements $ 111,510 $ 117,894 Furniture, fixtures and equipment 186,523 183,801 Software costs 115,631 103,842 413,664 405,537 Accumulated depreciation and amortization (291,811 ) (278,455 ) 121,853 127,082 Land 23,996 25,814 Construction in progress 15,029 3,549 $ 160,878 $ 156,445

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Instrument [Line Items]
Schedule of Debt	The following table sets forth WESCO’s outstanding indebtedness: As of December 31, 2018 2017 (In thousands) International lines of credit $ 30,785 $ 34,075 Term Loan Facility, less debt discount of $156 and $513 in 2018 and 2017, respectively 24,594 84,237 Accounts Receivable Securitization Facility 275,000 380,000 Revolving Credit Facility 51,598 12,000 5.375% Senior Notes due 2021 500,000 500,000 5.375% Senior Notes due 2024 350,000 350,000 Capital leases 1,123 1,959 Total debt 1,233,100 1,362,271 Less unamortized debt issuance costs (9,575 ) (13,711 ) Less short-term debt and current portion of long-term debt (56,214 ) (35,299 ) Total long-term debt $ 1,167,311 $ 1,313,261
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, 2018 : (In thousands) 2019 $ 56,702 2020 326,554 2021 500,000 2022 — 2023 — Thereafter 350,000 Total payments on debt 1,233,256 Debt discount (156 ) Total debt $ 1,233,100

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense	The following table sets forth the components of the provision (benefit) for income taxes: Year Ended December 31, 2018 2017 2016 (In thousands) Current income taxes: Federal (1) $ 28,464 $ 122,170 $ 65,614 State 7,458 2,259 6,489 Foreign 10,611 15,274 3,502 Total current income taxes 46,533 139,703 75,605 Deferred income taxes: Federal 5,253 (48,060 ) (42,835 ) State 1,967 4,508 (2,938 ) Foreign 1,917 (6,844 ) 599 Total deferred income taxes 9,137 (50,396 ) (45,174 ) Provision for income taxes $ 55,670 $ 89,307 $ 30,431
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, 2018 2017 2016 (In thousands) United States $ 198,556 $ 180,957 $ 80,881 Foreign 82,469 71,483 50,670 Income before income taxes $ 281,025 $ 252,440 $ 131,551
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, 2018 2017 2016 Federal statutory rate 21.0 % 35.0 % 35.0 % State income taxes, net of federal income tax benefit 2.8 1.4 1.0 Deemed repatriation of undistributed foreign earnings (1.2 ) 32.8 — Deferred income tax remeasurement (0.3 ) (22.4 ) — Tax effect of intercompany financing (5.6 ) (10.5 ) (19.9 ) Other (1) 3.1 (0.9 ) 7.0 Effective tax rate 19.8 % 35.4 % 23.1 %
Schedule of Deferred Tax Assets and Liabilities	The following table sets forth deferred tax assets and liabilities: As of December 31, 2018 2017 (In thousands) Assets Liabilities Assets Liabilities Accounts receivable $ 3,657 $ — $ 3,496 $ — Inventories — 3,315 — 3,181 Depreciation of property, buildings and equipment — 17,384 — 13,283 Amortization of intangible assets — 158,795 — 159,107 Employee benefits 20,107 — 14,835 — Stock-based compensation (1) 12,840 — 16,341 — Advance payments — — 8,456 — Tax loss carryforwards 15,557 — 19,128 — Other 7,927 4,115 11,850 8,672 Deferred income taxes before valuation allowance 60,088 183,609 74,106 184,243 Valuation allowance (4,072 ) — (2,518 ) — Total deferred income taxes $ 56,016 $ 183,609 $ 71,588 $ 184,243 (1) The Company does not expect the executive compensation deduction rules in Section 162(m) of the Internal Revenue Code as amended by the TCJA to have a material impact on the realizability of the deferred tax asset related to stock-based compensation.
Summary of Income Tax Examinations	The Company is under examination by tax authorities in the U.S. and Canada and remains subject to examination until the applicable statutes of limitation expire. The statutes of limitation for the material jurisdictions in which the Company files income tax returns remain open principally due to certain transfer pricing matters and are as follows: United States — Federal 2004 and forward United States — Material States 2004 and forward Canada 2004 and forward United States — Federal 2004 and forward United States — Material States 2004 and forward Canada 2004 and forward
Summary of Income Tax Contingencies	The following table sets forth the reconciliation of gross unrecognized tax benefits: As of December 31, 2018 2017 2016 (In thousands) Beginning balance January 1 $ 4,348 $ 6,181 $ 5,436 Additions for tax positions of prior years — — 3,298 Reductions for tax positions of prior years — (155 ) (21 ) Settlements (2,646 ) (1,025 ) (1,921 ) Lapse in statute of limitations (287 ) (755 ) (728 ) Foreign currency exchange rate changes (122 ) 102 117 Ending balance December 31 $ 1,293 $ 4,348 $ 6,181

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Year Ended December 31, 2018 2017 2016 (In thousands, except per share data) Net income attributable to WESCO International $ 227,343 $ 163,460 $ 101,588 Weighted-average common shares outstanding used in computing basic earnings per share 46,722 47,849 44,116 Common shares issuable upon exercise of dilutive equity awards 477 512 543 Common shares issuable from contingently convertible debentures (see below for basis of calculation) — — 3,674 Weighted-average common shares outstanding and common share equivalents used in computing diluted earnings per share 47,199 48,361 48,333 Earnings per share attributable to WESCO International Basic $ 4.87 $ 3.42 $ 2.30 Diluted $ 4.82 $ 3.38 $ 2.10

EMPLOYEE BENEFIT PLANS - (Table

EMPLOYEE BENEFIT PLANS - (Tables)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Schedule of Net Funded Status [Table Text Block]	The following tables present the changes in benefit obligations, plan assets and funded status for the pension plans and the components of net periodic pension cost. Year Ended December 31, (In thousands) 2018 2017 Accumulated Benefit Obligation (ABO) at December 31 $ 78,746 $ 92,375 Change in Projected Benefit Obligation (PBO) PBO at beginning of year $ 120,319 $ 96,160 Service cost 5,242 4,328 Interest cost 4,137 3,912 Participant contributions 745 735 Actuarial (gain) loss, including assumption changes (11,644 ) 10,906 Benefits paid (3,892 ) (3,005 ) Foreign currency exchange rate changes (9,392 ) 7,283 PBO at end of year $ 105,515 $ 120,319 Change in Plan Assets Fair value of plan assets at beginning of year $ 97,182 $ 84,753 Actual return on plan assets (425 ) 7,875 Participant contributions 745 735 Employer contributions 372 368 Benefits paid (3,892 ) (3,005 ) Foreign currency exchange rate changes (7,426 ) 6,456 Fair value of plan assets at end of year $ 86,556 $ 97,182 Funded Status $ (18,959 ) $ (23,137 ) Amounts Recognized in the Consolidated Balance Sheets Current liabilities $ (364 ) $ (395 ) Noncurrent liabilities (18,595 ) (22,742 ) Net amount recognized $ (18,959 ) $ (23,137 ) Amounts Recognized in Accumulated Other Comprehensive Income (Loss) Net actuarial (gain) loss $ (2,696 ) $ 2,508 Total amount recognized, before tax effect $ (2,696 ) $ 2,508
Schedule of Net Benefit Costs [Table Text Block]	Year Ended December 31, 2018 2017 2016 (In thousands) Components of Net Periodic Pension Cost Service cost $ 5,242 $ 4,328 $ 3,845 Interest cost 4,137 3,912 3,856 Expected return on plan assets (5,969 ) (5,562 ) (5,328 ) Recognized actuarial gain (46 ) (149 ) (31 ) Net periodic pension cost $ 3,364 $ 2,529 $ 2,342 Other Changes in Plan Assets and PBO Recognized in Accumulated Other Comprehensive Income (Loss) Net actuarial (gain) loss $ (5,250 ) $ 8,593 $ 2,756 Amortization of unrecognized net actuarial gain 46 149 31 Total amount recognized, before tax effect (5,204 ) 8,742 2,787 Tax effect 1,406 (2,361 ) (302 ) Total amount recognized, after tax effect $ (3,798 ) $ 6,381 $ 2,485 Total recognized in net periodic pension cost and accumulated other comprehensive income (loss) $ (434 ) $ 8,910 $ 4,827
Schedule of Allocation of Plan Assets [Table Text Block]	The asset mix is reviewed and rebalanced to target on an annual basis. Asset Category Target % Canadian equities 12.5 % Non-Canadian equities 27.5 % Total equities 40 % Fixed income investments 45 % Other investments 15 % The Plan's weighted asset allocations by asset category are as follows: December 31 2018 2017 Asset Category Pooled Funds: Canadian equities 12.4 % 11.5 % U.S. equities 5.0 % 4.6 % Non-North American equities 22.5 % 20.8 % Fixed income investments 44.7 % 41.4 % Other 15.4 % 21.7 % Total 100.0 % 100.0 %
Fair Value, Assets Measured on Recurring Basis [Table Text Block]	The following tables set forth the fair value of the Plan's assets by asset category: December 31, 2018 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Pooled Funds: Canadian equities $ — $ — $ — $ 10,693 $ 10,693 U.S. equities — — — 4,356 4,356 Non-North American equities — — — 19,492 19,492 Fixed income investments — — — 38,668 38,668 Other 203 — — 13,144 13,347 Total investments $ 203 $ — $ — $ 86,353 $ 86,556 December 31, 2017 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Pooled Funds: Canadian equities $ — $ — $ — $ 11,211 $ 11,211 U.S. equities — — — 4,436 4,436 Non-North American equities — — — 20,207 20,207 Fixed income investments — — — 40,193 40,193 Other 3,996 — — 17,139 21,135 Total investments $ 3,996 $ — $ — $ 93,186 $ 97,182 (1) As described above, investments measured at fair value using the NAV per share practical expedient have not been classified in the fair value hierarchy. The amounts presented in the tables are intended to reconcile the fair value hierarchy to the total fair value of plan assets.
Pension and Other Postretirement Plans, Pensions, Policy [Policy Text Block]	13. EMPLOYEE BENEFIT PLANS Defined Contribution Plans A majority of WESCO’s employees are covered by defined contribution retirement savings plans for their services rendered subsequent to WESCO’s formation. WESCO also offers a deferred compensation plan for select individuals. For U.S. participants, WESCO matches contributions made by employees at an amount equal to 50% of participants' total monthly contributions up to a maximum of 6% of eligible compensation. For Canadian participants, WESCO makes contributions in amounts ranging from 3% to 5% of participants' eligible compensation based on years of continuous service. WESCO may also make, subject to the Board's approval, a discretionary contribution to the defined contribution retirement savings plan covering U.S. participants if certain predetermined profit levels are attained. Discretionary employer contribution charges of $20.6 million and $10.0 million were incurred in 2018 and 2017 , respectively. In 2016 , there was no charge for discretionary employer contributions. For the years ended December 31, 2018 , 2017 and 2016 , WESCO incurred charges of $42.0 million , $31.3 million , and $18.5 million , respectively, for all such plans. Contributions are made in cash to employee retirement savings plan accounts. The deferred compensation plan is an unfunded plan. As of December 31, 2018 and 2017 , the Company's obligation under the deferred compensation plan was $21.9 million and $24.3 million , respectively. Employees have the option to transfer balances allocated to their accounts in the defined contribution retirement savings plan and the deferred compensation plan into any of the available investment options. Defined Benefit Plans The Company sponsors a contributory defined benefit plan (the "Plan") covering substantially all Canadian employees of EECOL. The Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the Plan. Participants become 100% vested after two years of continuous service or, if earlier, at the participant's normal retirement age. The Company also sponsors a Supplemental Executive Retirement Plan (the "SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the SERP was closed to new participants and existing participants became 100% vested. SERP participants continue to contribute 4% of their earnings to the Plan. The following tables present the changes in benefit obligations, plan assets and funded status for the pension plans and the components of net periodic pension cost. Year Ended December 31, (In thousands) 2018 2017 Accumulated Benefit Obligation (ABO) at December 31 $ 78,746 $ 92,375 Change in Projected Benefit Obligation (PBO) PBO at beginning of year $ 120,319 $ 96,160 Service cost 5,242 4,328 Interest cost 4,137 3,912 Participant contributions 745 735 Actuarial (gain) loss, including assumption changes (11,644 ) 10,906 Benefits paid (3,892 ) (3,005 ) Foreign currency exchange rate changes (9,392 ) 7,283 PBO at end of year $ 105,515 $ 120,319 Change in Plan Assets Fair value of plan assets at beginning of year $ 97,182 $ 84,753 Actual return on plan assets (425 ) 7,875 Participant contributions 745 735 Employer contributions 372 368 Benefits paid (3,892 ) (3,005 ) Foreign currency exchange rate changes (7,426 ) 6,456 Fair value of plan assets at end of year $ 86,556 $ 97,182 Funded Status $ (18,959 ) $ (23,137 ) Amounts Recognized in the Consolidated Balance Sheets Current liabilities $ (364 ) $ (395 ) Noncurrent liabilities (18,595 ) (22,742 ) Net amount recognized $ (18,959 ) $ (23,137 ) Amounts Recognized in Accumulated Other Comprehensive Income (Loss) Net actuarial (gain) loss $ (2,696 ) $ 2,508 Total amount recognized, before tax effect $ (2,696 ) $ 2,508 Year Ended December 31, 2018 2017 2016 (In thousands) Components of Net Periodic Pension Cost Service cost $ 5,242 $ 4,328 $ 3,845 Interest cost 4,137 3,912 3,856 Expected return on plan assets (5,969 ) (5,562 ) (5,328 ) Recognized actuarial gain (46 ) (149 ) (31 ) Net periodic pension cost $ 3,364 $ 2,529 $ 2,342 Other Changes in Plan Assets and PBO Recognized in Accumulated Other Comprehensive Income (Loss) Net actuarial (gain) loss $ (5,250 ) $ 8,593 $ 2,756 Amortization of unrecognized net actuarial gain 46 149 31 Total amount recognized, before tax effect (5,204 ) 8,742 2,787 Tax effect 1,406 (2,361 ) (302 ) Total amount recognized, after tax effect $ (3,798 ) $ 6,381 $ 2,485 Total recognized in net periodic pension cost and accumulated other comprehensive income (loss) $ (434 ) $ 8,910 $ 4,827 In accordance with ASU 2017-07, as described in Note 2, the service cost of $5.2 million , $4.3 million and $3.8 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, was reported as a component of selling, general and administrative expenses. The other components of net periodic benefit cost totaling a net benefit of $1.9 million for the year ended December 31, 2018 was presented as a component of net interest and other, as described in Note 15 below. For the years ended December 31, 2017 and 2016 , the Company reclassified a net benefit of $1.8 million and $1.5 million , respectively, from selling, general and administrative expenses to net interest and other. The Company used the amounts disclosed in Note 11 of the Notes to Consolidated Financial Statements in the Annual Report on Form 10-K for the fiscal year ended December 31, 2017 as the estimation basis for applying the retrospective presentation requirements. The interest rate used to discount future estimated cash flows is determined using the Canadian Institute of Actuaries ("CIA") methodology, which references yield curve information provided by Fiera Capital and matches expected benefit payments. The expected long-term rate of return on plan assets is applied to the fair market-related value of plan assets. The following weighted-average actuarial assumptions were used to determine benefit obligations at December 31: 2018 2017 Pension Plan SERP Pension Plan SERP Discount rate 4.0 % 4.0 % 3.5 % 3.5 % Rate of compensation increase 3.8 % 3.8 % 3.8 % 3.8 % The following weighted-average actuarial assumptions were used to determine net periodic pension costs at January 1: Year Ended December 31, 2018 2017 2016 Pension Plan SERP Pension Plan SERP Pension Plan SERP Discount rate 3.5 % 3.5 % 3.9 % 3.9 % 4.2 % 4.2 % Expected long-term return on assets 6.4 % n/a 6.4 % n/a 6.4 % n/a Rate of compensation increase 3.8 % 3.8 % 3.8 % 3.8 % 4.0 % 4.0 % The following benefit payments, which reflect expected future service, are expected to be paid: Years ending December 31 (In thousands) 2019 $ 2,870 2020 2,946 2021 3,098 2022 3,196 2023 3,448 2024 to 2028 21,721 The Company expects to contribute approximately $2.9 million and $0.4 million to the Plan and SERP, respectively, in 2019 . The Plan's weighted asset allocations by asset category are as follows: December 31 2018 2017 Asset Category Pooled Funds: Canadian equities 12.4 % 11.5 % U.S. equities 5.0 % 4.6 % Non-North American equities 22.5 % 20.8 % Fixed income investments 44.7 % 41.4 % Other 15.4 % 21.7 % Total 100.0 % 100.0 % The Plan's long-term overall objective is to maintain benefits at their current level without affecting the cost of maintaining the Plan, assuming that the demographic make-up of the group of members remains the same. The primary investment objective, in support of the overall objective, is to earn the highest rate of return possible for the Plan, while keeping risk at acceptable levels. The long-term return objective of the Plan is to achieve a minimum annualized rate of return in excess of the actuarial requirements. This translates into a required return of 3.0% above inflation, net of investment management fees. The return objective is consistent with the overall investment risk level that the Plan assumes in order to meet the pension obligations of the Plan. To achieve this long term investment objective, the Plan has adopted an asset mix that has a combination of primarily equity and fixed income investments. Risk is controlled by investing in a well-diversified portfolio of asset classes. A benchmark portfolio is established based on the expected returns for each asset class available. The investment of the Plan's assets in accordance with the benchmark portfolio should enable the Plan to not only attain, but also exceed the minimum overall objective. The following table presents the target asset mix based on market value for each investment category within which the investment managers must invest the Plan's assets. The asset mix is reviewed and rebalanced to target on an annual basis. Asset Category Target % Canadian equities 12.5 % Non-Canadian equities 27.5 % Total equities 40 % Fixed income investments 45 % Other investments 15 % The Plan's assets are measured at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities are classified in the fair value hierarchy based on the lowest level of any input that is significant to the measurement of fair value. Investments for which fair value is measured using the net asset value (NAV) per share practical expedient are not classified in the fair value hierarchy. The following describes the valuation methodologies used to measure the fair value of the Plan's assets. Pooled Equity Investments. These investments consist of the Plan's share of segregated funds that primarily invest in equity securities. The funds are valued at the net asset value of shares held in the underlying funds. Pooled Fixed Income Investments. These investments consist of the Plan's share of a segregated fund that primarily invests in Canadian issued bonds and debentures and is valued at the net asset value of shares held in the underlying securities. Other Investments. These investments consist of cash and cash equivalents, a money market fund and diversified growth funds. The diversified growth funds invest in a broad range of asset classes, including equities, bonds, infrastructure, property, commodities and absolute return strategies. These investments are valued at the net asset value of shares held in the underlying funds. The fair value methods described above may not be indicative of net realizable value or reflective of future fair values. Additionally, while the Company believes the valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. The following tables set forth the fair value of the Plan's assets by asset category: December 31, 2018 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Pooled Funds: Canadian equities $ — $ — $ — $ 10,693 $ 10,693 U.S. equities — — — 4,356 4,356 Non-North American equities — — — 19,492 19,492 Fixed income investments — — — 38,668 38,668 Other 203 — — 13,144 13,347 Total investments $ 203 $ — $ — $ 86,353 $ 86,556 December 31, 2017 (In thousands) Level 1 Level 2 Level 3 NAV (1) Total Pooled Funds: Canadian equities $ — $ — $ — $ 11,211 $ 11,211 U.S. equities — — — 4,436 4,436 Non-North American equities — — — 20,207 20,207 Fixed income investments — — — 40,193 40,193 Other 3,996 — — 17,139 21,135 Total investments $ 3,996 $ — $ — $ 93,186 $ 97,182 (1) As described above, investments measured at fair value using the NAV per share practical expedient have not been classified in the fair value hierarchy. The amounts presented in the tables are intended to reconcile the fair value hierarchy to the total fair value of plan assets.
Schedule of Assumptions Used [Table Text Block]	The following weighted-average actuarial assumptions were used to determine net periodic pension costs at January 1: Year Ended December 31, 2018 2017 2016 Pension Plan SERP Pension Plan SERP Pension Plan SERP Discount rate 3.5 % 3.5 % 3.9 % 3.9 % 4.2 % 4.2 % Expected long-term return on assets 6.4 % n/a 6.4 % n/a 6.4 % n/a Rate of compensation increase 3.8 % 3.8 % 3.8 % 3.8 % 4.0 % 4.0 % The following weighted-average actuarial assumptions were used to determine benefit obligations at December 31: 2018 2017 Pension Plan SERP Pension Plan SERP Discount rate 4.0 % 4.0 % 3.5 % 3.5 % Rate of compensation increase 3.8 % 3.8 % 3.8 % 3.8 %
Schedule of Expected Benefit Payments [Table Text Block]	The following benefit payments, which reflect expected future service, are expected to be paid: Years ending December 31 (In thousands) 2019 $ 2,870 2020 2,946 2021 3,098 2022 3,196 2023 3,448 2024 to 2028 21,721

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [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 years presented: Year Ended December 31, 2018 2017 2016 Awards Weighted-Average Exercise Price Weighted-Average Remaining Contractual Life Aggregate Intrinsic Value (In thousands) Awards Weighted-Average Exercise Price Awards Weighted-Average Exercise Price Beginning of year 2,238,607 $ 57.75 2,439,487 $ 52.62 2,567,021 $ 54.47 Granted 509,046 62.68 455,807 71.21 709,999 42.63 Exercised (192,700 ) 40.74 (495,181 ) 42.19 (526,818 ) 41.54 Canceled (203,320 ) 68.69 (161,506 ) 66.06 (310,715 ) 63.71 End of year 2,351,633 59.26 6.1 $ 6,514 2,238,607 57.75 2,439,487 52.62 Exercisable at end of year 1,453,932 $ 57.93 4.6 $ 5,623 1,331,580 $ 56.96 1,549,350 $ 53.35
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	the fair value of stock-settled stock appreciation rights granted during the years presented: Year Ended December 31, 2018 2017 2016 Stock-settled stock appreciation rights granted 509,046 455,807 709,999 Risk free interest rate 2.5% 1.9% 1.2% Expected life (in years) 5 5 5 Expected volatility 28% 29% 32%
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	The following table sets forth a summary of performance-based awards and related information for the years presented: Year Ended December 31, 2018 2017 2016 Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Unvested at beginning of year 148,508 $ 60.23 149,320 $ 60.36 114,520 $ 76.48 Granted 44,144 62.80 39,978 76.63 91,768 47.00 Vested — — — — — — Forfeited (53,756 ) 64.67 (40,790 ) 76.77 (56,968 ) 71.25 Unvested at end of year 138,896 $ 59.33 148,508 $ 60.23 149,320 $ 60.36 The following table sets forth a summary of time-based restricted stock units and related information for the years presented: Year Ended December 31, 2018 2017 2016 Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Awards Weighted-Average Fair Value Unvested at beginning of year 290,054 $ 58.11 257,096 $ 57.47 175,411 $ 74.52 Granted 122,062 62.40 100,993 71.33 162,256 44.45 Vested (64,166 ) 67.91 (44,720 ) 84.57 (60,015 ) 72.41 Forfeited (20,152 ) 58.15 (23,315 ) 57.52 (20,556 ) 59.15 Unvested at end of year 327,798 $ 57.87 290,054 $ 58.11 257,096 $ 57.47
Schedule of Share-based Payment Award, Performance-based Awards, Valuation Assumptions [Table Text Block]	The following table sets forth the assumptions used to estimate the fair value of performance shares granted during the years presented: Year ended December 31, 2018 2017 2016 Grant date share price $ 62.80 $ 71.67 $ 42.44 WESCO expected volatility n/a 29 % 26 % Peer group median volatility n/a 24 % 24 % Risk-free interest rate n/a 1.5 % 0.9 % Correlation of peer company returns n/a 114 % 122 %

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum rental payments required under operating leases, primarily for real property that have noncancelable lease terms in excess of one year as of December 31, 2018 , are as follows: Years ending December 31 (In thousands) 2019 $ 71,640 2020 59,594 2021 47,264 2022 34,490 2023 24,493 Thereafter 40,302

SEGMENTS AND RELATED INFORMAT_2

SEGMENTS AND RELATED INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	WESCO attributes revenues from external customers to individual countries on the basis of the point of sale. The following table sets forth information about WESCO by geographic area: Net Sales Year Ended December 31, Long-Lived Assets December 31, 2018 2017 2016 2018 2017 2016 (In thousands) United States $ 6,089,130 75 % $ 5,775,988 75 % $ 5,635,803 77 % $ 106,078 $ 95,851 $ 123,465 Other International (1) 2,087,471 25 % 1,903,033 25 % 1,700,214 23 % 54,800 60,594 65,182 Total $ 8,176,601 $ 7,679,021 $ 7,336,017 $ 160,878 $ 156,445 $ 188,647 (1) Other primarily includes Canada.
Revenue from External Customers by Products and Services	The following table sets forth information about WESCO’s sales by product category: Year Ended December 31, 2018 2017 2016 (percentages based on total sales) General Supplies 40% 40% 40% Wire, Cable and Conduit 14% 15% 14% Communications and Security 16% 15% 15% Electrical Distribution and Controls 11% 10% 11% Lighting and Sustainability 11% 12% 12% Automation, Controls and Motors 8% 8% 8%

OTHER FINANCIAL INFORMATION (Ta

OTHER FINANCIAL INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information [Abstract]
Condensed Balance Sheet [Table Text Block]	Condensed Consolidating Balance Sheet December 31, 2018 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Cash and cash equivalents $ — $ 35,931 $ 60,412 $ — $ 96,343 Trade accounts receivable, net — — 1,166,607 — 1,166,607 Inventories — 440,422 508,304 — 948,726 Prepaid expenses and other current assets 1,123 57,586 124,523 (9,268 ) 173,964 Total current assets 1,123 533,939 1,859,846 (9,268 ) 2,385,640 Intercompany receivables, net — — 2,403,704 (2,403,704 ) — Property, buildings and equipment, net — 63,506 97,372 — 160,878 Intangible assets, net — 2,131 313,885 — 316,016 Goodwill — 257,623 1,464,980 — 1,722,603 Investments in affiliates 3,182,469 5,137,783 (8,320,252 ) — Other assets — 2,905 16,994 19,899 Total assets $ 3,183,592 $ 5,997,887 $ 6,156,781 $ (10,733,224 ) $ 4,605,036 Accounts payable $ — $ 404,373 $ 389,975 $ — $ 794,348 Short-term debt — — 30,785 — 30,785 Other current liabilities — 86,600 159,481 (9,268 ) 236,813 Total current liabilities — 490,973 580,241 (9,268 ) 1,061,946 Intercompany payables, net 1,048,282 1,355,422 — (2,403,704 ) — Long-term debt — 842,093 325,218 — 1,167,311 Other noncurrent liabilities — 126,930 119,123 — 246,053 Total WESCO International stockholders’ equity 2,135,310 3,182,469 5,137,783 (8,320,252 ) 2,135,310 Noncontrolling interests — — (5,584 ) — (5,584 ) Total liabilities and stockholders’ equity $ 3,183,592 $ 5,997,887 $ 6,156,781 $ (10,733,224 ) $ 4,605,036 Condensed Consolidating Balance Sheet December 31, 2017 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Cash and cash equivalents $ — $ 50,602 $ 67,351 $ — $ 117,953 Trade accounts receivable, net — — 1,170,080 — 1,170,080 Inventories — 430,092 526,056 — 956,148 Prepaid expenses and other current assets 4,730 42,547 152,531 (35,140 ) 164,668 Total current assets 4,730 523,241 1,916,018 (35,140 ) 2,408,849 Intercompany receivables, net — — 2,189,136 (2,189,136 ) — Property, buildings and equipment, net — 50,198 106,247 — 156,445 Intangible assets, net — 2,770 364,334 — 367,104 Goodwill — 257,623 1,514,254 — 1,771,877 Investments in affiliates 3,058,613 5,023,826 — (8,082,439 ) — Other assets — 2,778 28,415 — 31,193 Total assets $ 3,063,343 $ 5,860,436 $ 6,118,404 $ (10,306,715 ) $ 4,735,468 Accounts payable $ — $ 417,690 $ 381,830 $ — $ 799,520 Short-term debt — — 34,075 — 34,075 Other current liabilities — 80,039 162,475 (35,140 ) 207,374 Total current liabilities — 497,729 578,380 (35,140 ) 1,040,969 Intercompany payables, net 939,784 1,249,352 — (2,189,136 ) — Long-term debt — 934,033 379,228 — 1,313,261 Other noncurrent liabilities 3,820 120,709 140,566 — 265,095 Total WESCO International stockholders’ equity 2,119,739 3,058,613 5,023,826 (8,082,439 ) 2,119,739 Noncontrolling interests — — (3,596 ) — (3,596 ) Total liabilities and stockholders’ equity $ 3,063,343 $ 5,860,436 $ 6,118,404 $ (10,306,715 ) $ 4,735,468
Condensed Income Statement [Table Text Block]	Condensed Consolidating Statement of Income and Comprehensive Income Year ended December 31, 2018 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net sales $ — $ 3,572,406 $ 4,757,321 $ (153,126 ) $ 8,176,601 Cost of goods sold (excluding depreciation and — 2,890,490 3,871,856 (153,126 ) 6,609,220 amortization) Selling, general and administrative expenses — 590,009 561,935 — 1,151,944 Depreciation and amortization — 18,334 44,663 — 62,997 Results of affiliates’ operations 225,355 209,802 — (435,157 ) — Net interest and other — 54,178 17,237 — 71,415 Provision for income taxes — 3,842 51,828 — 55,670 Net income 225,355 225,355 209,802 (435,157 ) 225,355 Less: Net loss attributable to noncontrolling interests — — (1,988 ) — (1,988 ) Net income attributable to WESCO International $ 225,355 $ 225,355 $ 211,790 $ (435,157 ) $ 227,343 Other comprehensive income (loss): Foreign currency translation adjustments (99,643 ) (99,643 ) (99,643 ) 199,286 (99,643 ) Post retirement benefit plan adjustments, net of tax 3,798 3,798 3,798 (7,596 ) 3,798 Comprehensive income attributable to WESCO International $ 129,510 $ 129,510 $ 115,945 $ (243,467 ) $ 131,498 Condensed Consolidating Statement of Income and Comprehensive Income Year ended December 31, 2017 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net sales $ — $ 3,370,088 $ 4,441,655 $ (132,722 ) $ 7,679,021 Cost of goods sold (excluding depreciation and — 2,714,511 3,612,577 (132,722 ) 6,194,366 amortization) Selling, general and administrative expenses — 555,503 546,095 — 1,101,598 Depreciation and amortization — 18,442 45,575 — 64,017 Results of affiliates’ operations 160,587 168,782 — (329,369 ) — Net interest and other — 94,313 (27,713 ) — 66,600 Provision for income taxes (2,546 ) (4,486 ) 96,339 — 89,307 Net income 163,133 160,587 168,782 (329,369 ) 163,133 Less: Net loss attributable to noncontrolling interests — — (327 ) — (327 ) Net income attributable to WESCO International $ 163,133 $ 160,587 $ 169,109 $ (329,369 ) $ 163,460 Other comprehensive income (loss): Foreign currency translation adjustments 85,762 85,762 85,762 (171,524 ) 85,762 Post retirement benefit plan adjustments, net of tax (6,381 ) (6,381 ) (6,381 ) 12,762 (6,381 ) Comprehensive income attributable to WESCO International $ 242,514 $ 239,968 $ 248,490 $ (488,131 ) $ 242,841 Condensed Consolidating Statement of Income and Comprehensive Income Year ended December 31, 2016 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net sales $ — $ 3,306,265 $ 4,134,508 $ (104,756 ) $ 7,336,017 Cost of goods sold (excluding depreciation and — 2,651,409 3,341,161 (104,756 ) 5,887,814 amortization) Selling, general and administrative expenses 61 477,437 573,301 — 1,050,799 Depreciation and amortization — 20,226 46,632 — 66,858 Results of affiliates’ operations 240,571 155,814 — (396,385 ) — Net interest and other 17,555 87,824 (30,317 ) — 75,062 Loss on debt redemption 123,933 — — — 123,933 Provision for income taxes (2,098 ) 8,263 24,266 — 30,431 Net income $ 101,120 $ 216,920 $ 179,465 $ (396,385 ) $ 101,120 Less: Net loss attributable to noncontrolling interests — — (468 ) — (468 ) Net income attributable to WESCO International $ 101,120 $ 216,920 $ 179,933 $ (396,385 ) $ 101,588 Other comprehensive income (loss): Foreign currency translation adjustments 38,275 38,275 38,275 (76,550 ) 38,275 Post retirement benefit plan adjustments, net of tax (2,485 ) (2,485 ) (2,485 ) 4,970 (2,485 ) Comprehensive income attributable to WESCO International $ 136,910 $ 252,710 $ 215,723 $ (467,965 ) $ 137,378
Condensed Cash Flow Statement [Table Text Block]	Condensed Consolidating Statement of Cash Flows Year ended December 31, 2017 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net cash (used in) provided by operating activities $ (36,575 ) $ 101,826 $ 83,871 $ — $ 149,122 Investing activities: Capital expenditures — (13,215 ) (8,292 ) — (21,507 ) Proceeds from sale of assets — — 6,766 — 6,766 Dividends received from subsidiaries — 307,784 — (307,784 ) — Advances to subsidiaries and other — (383,686 ) 26,912 366,220 9,446 Net cash (used in) provided by investing activities — (89,117 ) 25,386 58,436 (5,295 ) Financing activities: Proceeds from issuance of debt 143,367 775,926 1,144,848 (383,686 ) 1,680,455 Repayments of debt — (785,392 ) (952,740 ) 17,466 (1,720,666 ) Equity activities (106,792 ) — — — (106,792 ) Dividends paid by subsidiaries — — (307,784 ) 307,784 — Other — 5,807 — — 5,807 Net cash provided by (used in) financing activities 36,575 (3,659 ) (115,676 ) (58,436 ) (141,196 ) Effect of exchange rate changes on cash and cash equivalents — — 5,191 — 5,191 Net change in cash and cash equivalents — 9,050 (1,228 ) — 7,822 Cash and cash equivalents at the beginning of period — 41,552 68,579 — 110,131 Cash and cash equivalents at the end of period $ — $ 50,602 $ 67,351 $ — $ 117,953 Condensed Consolidating Statement of Cash Flows Year ended December 31, 2018 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net cash provided by operating activities $ 18,672 $ 153,467 $ 124,582 $ — $ 296,721 Investing activities: Capital expenditures — (17,573 ) (18,637 ) — (36,210 ) Proceeds from sale of assets — — 12,461 — 12,461 Dividends received from subsidiaries 347,531 (347,531 ) — Advances to subsidiaries and other — (406,028 ) 196,219 199,416 (10,393 ) Net cash (used in) provided by investing activities — (76,070 ) 190,043 (148,115 ) (34,142 ) Financing activities: Proceeds from issuance of debt 108,497 339,606 1,086,673 (199,416 ) 1,335,360 Repayments of debt — (410,606 ) (1,051,611 ) — (1,462,217 ) Equity activities (127,169 ) — — — (127,169 ) Dividends paid by subsidiaries (347,531 ) 347,531 — Other — (21,068 ) — — (21,068 ) Net cash used in financing activities (18,672 ) (92,068 ) (312,469 ) 148,115 (275,094 ) Effect of exchange rate changes on cash and cash equivalents (9,095 ) — (9,095 ) Net change in cash and cash equivalents — (14,671 ) (6,939 ) — (21,610 ) Cash and cash equivalents at the beginning of period — 50,602 67,351 — 117,953 Cash and cash equivalents at the end of period $ — $ 35,931 $ 60,412 $ — $ 96,343 Condensed Consolidating Statement of Cash Flows Year ended December 31, 2016 (In thousands) WESCO International, Inc. WESCO Distribution, Inc. Non-Guarantor Subsidiaries Consolidating and Eliminating Entries Consolidated Net cash provided by (used in) operating activities $ 95,388 $ (243,476 ) $ 448,323 $ — $ 300,235 Investing activities: Capital expenditures — (12,482 ) (5,475 ) — (17,957 ) Acquisition payments, net of cash acquired — (50,890 ) — — (50,890 ) Proceeds from sale of assets — — 8,361 — 8,361 Dividends received from subsidiaries — 82,912 — (82,912 ) — Advances to subsidiaries and other — (297,259 ) (337,344 ) 624,603 (10,000 ) Net cash used in investing activities — (277,719 ) (334,458 ) 541,691 (70,486 ) Financing activities: Proceeds from issuance of debt 252,246 1,566,864 672,345 (297,259 ) 2,194,196 Repayments of debt (344,804 ) (1,030,520 ) (752,401 ) (327,344 ) (2,455,069 ) Equity activities (2,830 ) — — — (2,830 ) Dividends paid by subsidiaries — — (82,912 ) 82,912 — Other — (12,560 ) — — (12,560 ) Net cash (used in) provided by financing activities (95,388 ) 523,784 (162,968 ) (541,691 ) (276,263 ) Effect of exchange rate changes on cash and cash equivalents — — (3,634 ) — (3,634 ) Net change in cash and cash equivalents — 2,589 (52,737 ) — (50,148 ) Cash and cash equivalents at the beginning of period — 38,963 121,316 — 160,279 Cash and cash equivalents at the end of period $ — $ 41,552 $ 68,579 $ — $ 110,131

SELECTED QUARTERLY FINANCIAL _2

SELECTED QUARTERLY FINANCIAL DATA (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	First Quarter Second Quarter Third Quarter Fourth Quarter 2018 Net Sales $ 1,993,915 $ 2,103,994 $ 2,067,245 $ 2,011,447 Cost of goods sold (excluding depreciation and amortization) 1,613,966 1,704,100 1,670,037 1,621,117 Income from operations 73,241 91,183 97,517 90,499 Income before income taxes 53,458 73,442 80,467 73,658 Net income 42,971 57,673 66,645 58,066 Net income attributable to WESCO International 44,421 57,940 66,849 58,133 Basic earnings per share attributable to WESCO International (2) 0.94 1.23 1.42 1.27 Diluted earnings per share attributable to WESCO International (3) 0.93 1.22 1.41 1.26 2017 Net Sales $ 1,772,591 $ 1,909,624 $ 2,000,159 $ 1,996,647 Cost of goods sold (excluding depreciation and amortization) 1,422,573 1,543,510 1,614,814 1,613,469 Income from operations 67,089 83,105 89,250 81,446 Income before income taxes 50,368 66,289 71,939 63,844 Net income (1) 37,800 49,535 53,576 22,222 Net income attributable to WESCO International (1) 37,729 49,510 53,675 22,546 Basic earnings per share attributable to WESCO International (1) (2) 0.77 1.03 1.13 0.48 Diluted earnings per share attributable to WESCO International (1) (3) 0.76 1.02 1.12 0.47

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Allowance for Doubtful Accounts	Balance at Beginning Charged to Charged to Other Balance at of Period Expense Accounts (1) Deductions (2) End of Period Allowance for doubtful accounts (In thousands) Year ended December 31, 2018 $ 21,313 10,854 — (7,699 ) $ 24,468 Year ended December 31, 2017 22,007 8,466 — (9,160 ) 21,313 Year ended December 31, 2016 22,587 5,888 21 (6,489 ) 22,007 _________________________ (1) Represents allowance for doubtful accounts in connection with certain acquisitions and divestitures. (2) Includes a reduction in the allowance for doubtful accounts due to write-off of accounts receivable.

REVENUE (Tables)

REVENUE (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	The following tables disaggregate WESCO’s net sales by end market and geography: Year Ended December 31, (In thousands) 2018 2017 2016 Industrial $ 2,983,062 $ 2,852,357 $ 2,644,442 Construction 2,684,844 2,546,261 2,482,624 Utility 1,303,697 1,181,704 1,158,651 Commercial, Institutional and Government 1,204,998 1,098,699 1,050,300 Total by end market $ 8,176,601 $ 7,679,021 $ 7,336,017 Year Ended December 31, (In thousands) 2018 2017 2016 United States $ 6,089,130 $ 5,775,988 $ 5,635,803 Other (1) 2,087,471 1,903,033 1,700,214 Total by geography $ 8,176,601 $ 7,679,021 $ 7,336,017 (1) Other primarily includes net sales originating in Canada.

ORGANIZATION (Details)

ORGANIZATION (Details)	12 Months Ended
	Dec. 31, 2018customerscountriesbranches
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Customers (in customers) | customers	70,000
Full service branches (in branches) | branches	500
Distribution Centers	10
Additional countries (in countries) | countries	15

ACCOUNTING POLICIES - GENERAL (

ACCOUNTING POLICIES - GENERAL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 27, 2009
Defined Benefit Plan Disclosure
Income Taxes Receivable, Current	$ 24,873	$ 23,250
Prepaid Expense and Other Assets, Current	52,107	40,189
Assets, Current	2,385,640	2,408,849
Intangible Assets, Net (Including Goodwill)	$ 1,800,000	1,900,000
Characteristics of Securitizations or Asset-backed Financing Arrangements that are Accounted for as Sale	Under the Receivables Facility, WESCO sells, on a continuous basis, an undivided interest in all domestic accounts receivable to WESCO Receivables, a wholly owned special purpose entity (the “SPE”). The SPE sells, without recourse, a senior undivided interest in the receivables to financial institutions for cash while maintaining a subordinated undivided interest in the receivables, in the form of overcollateralization. Since WESCO maintains control of the transferred receivables, the transfers do not qualify for “sale” treatment. As a result, the transferred receivables remain on the balance sheet, and WESCO recognizes the related secured borrowing. WESCO has agreed to continue servicing the sold receivables for the third-party conduits and financial institutions at market rates; accordingly, no servicing asset or liability has been recorded. The expenses associated with the Receivables Facility are reported as a component of net interest and other in the Consolidated Statements of Income and Comprehensive Income.
Self Insurance Reserve	$ 13,100	13,900
Allowance for Doubtful Accounts Receivable, Current	24,468	21,313
Provision for Doubtful Accounts	10,900	8,500	$ 5,900
Inventory Valuation Reserves	27,600	28,600
Inventory Write-down	9,700	8,800	7,300
General and Administrative Costs in Inventory, Amount Incurred	69,200	70,700
Increase in deferred charges	0	915	6,002
Deferred Finance Costs, Net	9,575	13,711
Stock-based compensation expense	16,445	14,809	12,493
Goodwill	1,722,603	1,771,877	1,730,950
Assets	4,605,036	4,735,468
Liabilities, Current	1,061,946	1,040,969
Deferred Tax Liabilities, Net, Noncurrent	143,967	136,858
Liabilities	2,475,310	2,619,325
Retained Earnings (Accumulated Deficit)	2,307,462	2,079,697	1,914,757	$ 1,812,681
Accumulated Other Comprehensive Income (Loss), Net of Tax	(408,435)	(312,590)	$ (391,971)	$ (427,761)
Stockholders' Equity Attributable to Parent	2,135,310	2,119,739
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,129,726	2,116,143
Liabilities and Equity	$ 4,605,036	$ 4,735,468
Pension Plan [Member]
Defined Benefit Plan Disclosure
Discount rate	4.00%	3.50%
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
Convertible Debt
Defined Benefit Plan Disclosure
Debt Instrument, Face Amount					$ 345,000

ACCOUNTING POLICIES - PPE (Deta

ACCOUNTING POLICIES - PPE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Intangible Assets, Net (Including Goodwill)	$ 1,800,000	$ 1,900,000
Property, buildings and equipment, net	$ 160,878	$ 156,445
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	five to forty years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	three to ten years
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	three to five years
Land, Buildings and Improvements
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, net	$ 88,300

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - TEXTUALS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Finite-Lived Intangible Assets, Amortization Expense	$ 35.9	$ 37.8	$ 39.1

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF GOODWILL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Beginning balance January 1	$ 1,771,877	$ 1,730,950
Goodwill, Translation Adjustments	(49,274)	40,927
Ending balance December 31	$ 1,722,603	$ 1,771,877

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, 2018	Dec. 31, 2017
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ (249,539)	$ (223,554)
Intangible Assets Gross Excluding Goodwill	565,555	590,658
Intangible Assets, Net (Excluding Goodwill)	316,016	367,104
Trademarks
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	25,185	25,118
Finite-Lived Intangible Assets, Accumulated Amortization	(7,585)	(5,516)
Finite-Lived Intangible Assets, Net	17,600	19,602
Non-compete agreements
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	196	196
Finite-Lived Intangible Assets, Accumulated Amortization	(141)	(102)
Finite-Lived Intangible Assets, Net	55	94
Customer relationships
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	358,620	377,270
Finite-Lived Intangible Assets, Accumulated Amortization	(180,395)	(161,711)
Finite-Lived Intangible Assets, Net	178,225	215,559
Distribution agreements
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	36,984	39,515
Finite-Lived Intangible Assets, Accumulated Amortization	(22,562)	(22,200)
Finite-Lived Intangible Assets, Net	14,422	17,315
Patents
Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	48,310	48,310
Finite-Lived Intangible Assets, Accumulated Amortization	(38,856)	(34,025)
Finite-Lived Intangible Assets, Net	$ 9,454	14,285
Finite-Lived Intangible Assets, Useful Life, Minimum	10 years
Trademarks
Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets, Gross	$ 96,260	$ 100,249
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	4 years
Minimum | Non-compete agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Minimum | Customer relationships
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Minimum | Distribution agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Maximum
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Maximum | Trademarks
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	15 years
Maximum | Non-compete agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Maximum | Customer relationships
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years
Maximum | Distribution agreements
Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	19 years

GOODWILL AND INTANGIBLE ASSET_5

GOODWILL AND INTANGIBLE ASSETS - SCHEDULE OF EXPECTED AMORTIZATION EXPENSE (Details) $ in Thousands	Dec. 31, 2018USD ($)
Finite-Lived Intangible Assets, Future Amortization Expense [Abstract]
2,014	$ 35,269
2,015	33,417
2,016	25,809
2,017	23,431
2,018	22,877
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 78,953

CONCENTRATIONS OF CREDIT RISK_2

CONCENTRATIONS OF CREDIT RISK AND SIGNIFICANT SUPPLIERS (Details)	12 Months Ended
	Dec. 31, 2018
Supplier Concentration Risk | Cost of Goods, Total
Concentration Risk [Line Items]
Concentration Risk, Percentage	0.00%

ACQUISITIONS - ACQUISITIONS (De

ACQUISITIONS - ACQUISITIONS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)branches	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Number of Stores | branches	500
Net loss attributable to noncontrolling interest	$ (1,988)	$ (327)	$ (468)
Payments to Acquire Businesses, Gross			$ 51,922
Atlanta Electrical Distributors, LLC (AED) [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Mar. 14, 2016
Business Acquisition, Name of Acquired Entity	Atlanta Electrical Distributors, LLC
Number of Stores	5
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period	$ 85,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	21,800
Goodwill, Acquired During Period	$ 30,000
Trademarks | Atlanta Electrical Distributors, LLC (AED) [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	13 years
Finite-lived Intangible Assets Acquired	$ 6,000
Customer Relationships | Atlanta Electrical Distributors, LLC (AED) [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 15,800
Noncompete Agreements [Member] | Atlanta Electrical Distributors, LLC (AED) [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Finite-lived Intangible Assets Acquired	$ 100
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] | Customer Relationships | Atlanta Electrical Distributors, LLC (AED) [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	14 years
Maximum [Member] | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 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	4 years
Minimum | Customer Relationships
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Minimum | Customer Relationships | Atlanta Electrical Distributors, LLC (AED) [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	13 years
Minimum | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years

ACQUISITIONS - SCHEDULE OF BUSI

ACQUISITIONS - SCHEDULE OF BUSINESS ACQUISTIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			$ 76,980
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			25,058
Cash paid for acquisitions			51,922
Cash Acquired from Acquisition			(1,032)
Supplemental cash flow disclosure related to acquisitions:
Payments to Acquire Businesses, Net of Cash Acquired	$ 0	$ 0	$ 50,890

ACQUISITIONS - SCHEDULE OF PURC

ACQUISITIONS - SCHEDULE OF PURCHASE PRICE ALLOCATION (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets Acquired
Goodwill	$ 1,722,603	$ 1,771,877	$ 1,730,950
Total assets acquired			76,980
Liabilities Assumed
Total liabilities assumed			$ 25,058

PROPERTY, BUILDINGS AND EQUIP_3

PROPERTY, BUILDINGS AND EQUIPMENT - SCHEDULE OF PROPERTY, BUILDINGS AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (291,811)	$ (278,455)
Property, buildings and equipment, net	160,878	156,445
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	111,510	117,894
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	186,523	183,801
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	115,631	103,842
Depreciable [Member]
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	413,664	405,537
Property, buildings and equipment, net	121,853	127,082
Land
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	23,996	25,814
Construction in progress
Property, Plant and Equipment [Line Items]
Property, buildings and equipment, gross	$ 15,029	$ 3,549

PROPERTY, BUILDINGS AND EQUIP_4

PROPERTY, BUILDINGS AND EQUIPMENT - PROPERTY, BUILDINGS AND EQUIPMENT (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 17.3	$ 16.3	$ 17.1
Capitalized software amortization	9.8	9.9	$ 10.6
Unamortized software cost	24.2	22.4
Capitalized leases	9.3	10.6
Accumulated amortization related to capitalized leases	$ 8.4	$ 9

DEBT - SCHEDULE OF DEBT (Detail

DEBT - SCHEDULE OF DEBT (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Aug. 27, 2009
Debt Instrument [Line Items]
Long-term debt	$ 1,233,100
Total debt	1,233,100	$ 1,362,271
Debt Issuance Costs, Net	(9,575)	(13,711)
Less current and short-term portion	56,214	35,299
Total long-term debt	1,167,311	1,313,261
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt	24,594	84,237
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	500,000
Long-term debt	500,000	500,000
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	350,000
Long-term debt	$ 350,000	350,000
Accounts receivable securitization facility
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	1.95%
Long-term debt	$ 275,000	380,000
Revolving credit facility
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	3.46%
Long-term debt	$ 51,598	12,000
Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Long-term debt	$ 30,785	34,075
Convertible Debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 345,000
Debt Instrument, Interest Rate, Effective Percentage	13.875%
Capital leases
Debt Instrument [Line Items]
Long-term debt	$ 1,123	$ 1,959
United States | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	7.50%
Debt Instrument, Face Amount	$ 700,000
Debt Instrument, Interest Rate, Effective Percentage	1.00%

DEBT - DEBT (Details)

DEBT - DEBT (Details) - USD ($) $ / shares in Units, $ in Thousands	8 Months Ended	12 Months Ended							24 Months Ended
	Aug. 27, 2009	Jun. 14, 2022	Jun. 14, 2021	Jun. 14, 2020	Dec. 14, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 15, 2024	Dec. 15, 2021
Debt Instrument [Line Items]
Accounts Receivable from Securitization						$ 275,000	$ 380,000
Long-term debt						1,233,100
Gain (Loss) on Extinguishment of Debt						0	0	$ 123,933
Debt discount on convertible debentures						(156)
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	$ 106,500							(139,765)
Debt Instrument, Convertible, Carrying Amount of Equity Component						344,800
Amortization of Financing Costs and Discounts						$ 4,482	3,984	6,684
Debt Instrument, Call Date, Earliest						Sep. 15, 2016
2,014						$ 35,269
2,015						33,417
2,016						25,809
2,017						23,431
2,018						$ 22,877
Debt Instrument, Convertible, Terms of Conversion Feature						Holders who surrendered the 2029 Debentures for conversion received 18 shares of WESCO stock for each $1,000 principal amount of 2029 Debentures converted.
Debt Conversion, Converted Instrument, Shares Issued						6,267,688
Debt Issuance Costs, Net						$ 9,575	$ 13,711
Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate						8.78%	5.42%
Long-term debt						$ 30,785	$ 34,075
Term Loan Facility
Debt Instrument [Line Items]
Debt discount on convertible debentures						(156)	(513)
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt						$ 500,000	500,000
Debt Instrument, Interest Rate, Stated Percentage						5.375%
Deferred Finance Costs, Gross						$ 8,400
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed						101.00%
Debt Instrument, Face Amount						$ 500,000
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt						$ 350,000	350,000
Debt Instrument, Interest Rate, Stated Percentage						5.375%
Deferred Finance Costs, Gross						$ 6,000
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed						101.00%
Debt Instrument, Face Amount						$ 350,000
Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date						Dec. 12, 2012
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum						On November 19, 2013, the Borrowers and WESCO International entered into an amendment (the “Term Loan Amendment”) to the Term Loan Agreement. The Term Loan Amendment, among other things, reduced the applicable margin on U.S. term loans by 0.50% and the LIBOR floor applicable to the U.S. sub-facility from 1.00% to 0.75%. The modified pricing terms were effective December 13, 2013.
Debt Instrument, Unused Borrowing Capacity, Amount						$ 300,000
Debt Instrument, Decrease, Repayments						500,000
Long-term debt						$ 24,594	84,237
Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Amendment Description						On November 8, 2017, WESCO Distribution amended its accounts receivable securitization facility (the "Receivables Facility") pursuant to the terms and conditions of a Fifth Amendment to Fourth Amended and Restated Receivables Purchase Agreement, by and among WESCO Receivables Corp. (“WESCO Receivables”), WESCO Distribution, the various purchasers from time to time party thereto and PNC Bank, National Association, as Administrator (the "Amendment"). The Amendment extended the term of the Receivables Facility to September 24, 2020 and added and amended certain other defined terms. Substantially all other terms and conditions of the Receivables Facility were unchanged.
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate						1.95%
Accounts Receivable Eligible for Securitization						$ 758,300	751,200
Debt Instrument, Unused Borrowing Capacity, Amount						550,000
Long-term debt						$ 275,000	380,000
Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Borrowing Capacity, Description						On September 24, 2015, WESCO International, WESCO Distribution and certain other subsidiaries of the Company entered into a $600 million revolving credit facility (the “Revolving Credit Facility”), which contains a letter of credit sub-facility of up to $125 million, pursuant to the terms and conditions of a Second Amended and Restated Credit Agreement (the "Credit Agreement"). The Revolving Credit Facility contains an accordion feature allowing WESCO Distribution to request increases to the borrowing commitments of up to $200 million in the aggregate, subject to customary conditions.
Debt Instrument, Maturity Date						Sep. 1, 2020
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate						3.46%
Debt Instrument, Increase, Additional Borrowings						$ 473,100	834,400
Debt Instrument, Decrease, Repayments						433,500	826,400
Long-term debt						51,598	12,000
Line of Credit Facility, Remaining Borrowing Capacity						$ 515,900	562,900
Convertible Debt
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End						13.875%
Debt Instrument, Face Amount	345,000
Debt discount on convertible debentures	$ (181,200)
Amortization of Financing Costs and Discounts								$ 3,100
Canada | Secured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate at Period End						2.00%
Debt Instrument, Face Amount						$ 150,000
Canada | Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 400,000
United States | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate						7.50%
Debt Instrument, Interest Rate at Period End						1.00%
Long-term Debt, Gross						$ 24,800
Debt Instrument, Face Amount						700,000
United States | Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity						600,000
Minimum | Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 2,000
Minimum | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.95%
Maximum | Foreign Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity						$ 21,000
Maximum | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						0.45%
Accordion Feature [Member] | Accounts Receivable Securitization Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount						$ 100,000
Standby Letters of Credit [Member] | Revolving credit facility
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity						$ 18,000	$ 27,200
Common Stock
Debt Instrument [Line Items]
Common Stock, Par or Stated Value Per Share						$ 0.01	$ 0.01
London Interbank Offered Rate (LIBOR) [Member] | Minimum | Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						1.25%
London Interbank Offered Rate (LIBOR) [Member] | Maximum | Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						1.75%
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						0.75%
Scenario, Forecast [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed					101.344%					100.00%
Scenario, Forecast [Member] | Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed		101.344%	102.688%	104.031%					100.00%
Surety Bond [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity						$ 19,500	$ 19,100
Property Lease Guarantee [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity						$ 5,300	$ 7,100

DEBT - OUTSTANDING CONVERTIBLE

DEBT - OUTSTANDING CONVERTIBLE DEBENTURE SCHEDULE (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Aug. 27, 2009
Debt Instrument [Line Items]
Principal Balance	$ 1,233,256
Debt Instrument, Unamortized Discount	(156)
Total long-term debt	$ 1,233,100
Convertible Debt
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount		$ (181,200)

DEBT - SCHEDULE OF MATURITIES O

DEBT - SCHEDULE OF MATURITIES OF LONG-TERM DEBT (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Disclosure [Abstract]
2,013	$ 56,702
2,014	326,554
2,015	500,000
2,016	0
2,017	0
Thereafter	350,000
Total payments on debt	1,233,256
Debt discount on convertible debentures	(156)
Total long-term debt	$ 1,233,100

CAPITAL STOCK (Details)

CAPITAL STOCK (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	20,000,000	20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Debt Instrument, Convertible, Carrying Amount of Equity Component	$ 344.8
Common Stock
Class of Stock [Line Items]
Common Stock, Shares Authorized	210,000,000	210,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Class B
Class of Stock [Line Items]
Common Stock, Shares Authorized	20,000,000	20,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01

INCOME TAXES - ADDITIONAL INFO

INCOME TAXES - ADDITIONAL INFORMATION (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Deferred Income Tax Expense (Benefit)	$ 900	$ 56,400
Income Tax Examination, Description	<div style="line-height:120%;padding-top:8px;text-align:justify;text-indent:18px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">The Company is under examination by tax authorities in the U.S. and Canada and remains subject to examination until the applicable statutes of limitation expire. The statutes of limitation for the material jurisdictions in which the Company files income tax returns remain open principally due to certain transfer pricing matters and are as follows:</font></div><div style="line-height:120%;font-size:10pt;"><div style="padding-left:0px;text-indent:0px;line-height:normal;padding-top:10px;"><table cellpadding="0" cellspacing="0" style="font-family:Times New Roman;font-size:10pt;width:99.80506822612085%;border-collapse:collapse;text-align:left;"><tr><td colspan="3" rowspan="1"></td></tr><tr><td style="width:49%;" rowspan="1" colspan="1"></td><td style="width:1%;" rowspan="1" colspan="1"></td><td style="width:50%;" rowspan="1" colspan="1"></td></tr><tr><td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">United States — Federal</font></div></td><td style="vertical-align:bottom;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">2004 and forward</font></div></td></tr><tr><td style="vertical-align:top;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">United States — Material States</font></div></td><td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:top;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">2004 and forward</font></div></td></tr><tr><td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Canada</font></div></td><td style="vertical-align:bottom;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="overflow:hidden;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div></td><td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1"><div style="text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">2004 and forward</font></div></td></tr></table></div></div></div>" id="sjs-B5">&lt;div style="font-family:Times New Roman;font-size:10pt;">&lt;div style="line-height:120%;padding-top:8px;text-align:justify;text-indent:18px;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">The Company is under examination by tax authorities in the U.S. and Canada and remains subject to examination until the applicable statutes of limitation expire. The statutes of limitation for the material jurisdictions in which the Company files income tax returns remain open principally due to certain transfer pricing matters and are as follows:&lt;/font>&lt;/div>&lt;div style="line-height:120%;font-size:10pt;">&lt;div style="padding-left:0px;text-indent:0px;line-height:normal;padding-top:10px;">&lt;table cellpadding="0" cellspacing="0" style="font-family:Times New Roman;font-size:10pt;width:99.80506822612085%;border-collapse:collapse;text-align:left;">&lt;tr>&lt;td colspan="3" rowspan="1">&lt;/td>&lt;/tr>&lt;tr>&lt;td style="width:49%;" rowspan="1" colspan="1">&lt;/td>&lt;td style="width:1%;" rowspan="1" colspan="1">&lt;/td>&lt;td style="width:50%;" rowspan="1" colspan="1">&lt;/td>&lt;/tr>&lt;tr>&lt;td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="text-align:left;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">United States &#8212; Federal&lt;/font>&lt;/div>&lt;/td>&lt;td style="vertical-align:bottom;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="overflow:hidden;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">&#160;&lt;/font>&lt;/div>&lt;/td>&lt;td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="text-align:left;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">2004 and forward&lt;/font>&lt;/div>&lt;/td>&lt;/tr>&lt;tr>&lt;td style="vertical-align:top;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="text-align:left;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">United States &#8212; Material States&lt;/font>&lt;/div>&lt;/td>&lt;td style="vertical-align:bottom;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="overflow:hidden;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">&#160;&lt;/font>&lt;/div>&lt;/td>&lt;td style="vertical-align:top;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="text-align:left;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">2004 and forward&lt;/font>&lt;/div>&lt;/td>&lt;/tr>&lt;tr>&lt;td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="text-align:left;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">Canada&lt;/font>&lt;/div>&lt;/td>&lt;td style="vertical-align:bottom;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="overflow:hidden;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">&#160;&lt;/font>&lt;/div>&lt;/td>&lt;td style="vertical-align:top;background-color:#cceeff;padding-left:2px;padding-top:2px;padding-bottom:2px;padding-right:2px;" rowspan="1" colspan="1">&lt;div style="text-align:left;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">2004 and forward&lt;/font>&lt;/div>&lt;/td>&lt;/tr>&lt;/table>&lt;/div>&lt;/div>&lt;/div>
Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation			$ (100)
Deferred Tax Assets, Operating Loss Carryforwards	$ 15,557	19,128
Unrecognized Tax Benefits	1,293	4,348	6,181	$ 5,436
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	1,300	1,700	$ 7,500
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	100
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ 800	$ 1,800
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 3,400	$ 82,800
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Taxes Payable	43,200	65,000
Canada Revenue Agency [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	6,400	10,400
Unrecognized Tax Benefits		4,300	$ 6,200
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	7,200	7,000
Deferred Tax Assets, Tax Credit Carryforwards		17,800
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	$ 3,200	$ 3,100
Minimum | Canada Revenue Agency [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2036
Minimum | Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2019
Minimum | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2022

INCOME TAXES - SCHEDULE OF COMP

INCOME TAXES - SCHEDULE OF COMPONENTS OF INCOME TAX EXPENSE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 900	$ 56,400
Current taxes
Federal	28,464	122,170	$ 65,614
State	7,458	2,259	6,489
Foreign	10,611	15,274	3,502
Total current	46,533	139,703	75,605
Deferred taxes
Federal	5,253	(48,060)	(42,835)
State	1,967	4,508	(2,938)
Foreign	1,917	(6,844)	599
Total deferred	9,137	(50,396)	(45,174)
Income tax expense	$ 55,670	$ 89,307	$ 30,431

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States									$ 198,556	$ 180,957	$ 80,881
Foreign									82,469	71,483	50,670
Income before income taxes	$ 73,658	$ 80,467	$ 73,442	$ 53,458	$ 63,844	$ 71,939	$ 66,289	$ 50,368	$ 281,025	$ 252,440	$ 131,551

INCOME TAXES - SCHEDULE OF EFFE

INCOME TAXES - SCHEDULE OF EFFECTIVE INCOME TAX RATE RECONCILIATION (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0.9	$ 56.4
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 3.4	$ 82.8
Federal statutory rate	21.00%	35.00%	35.00%
State taxes, net of federal tax benefit	2.80%	1.40%	1.00%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	1.20%	32.80%	0.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	(0.30%)	(22.40%)	0.00%
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent	(5.60%)	(10.50%)	(19.90%)
Other	3.10%	(0.90%)	7.00%
Effective income tax rate	19.80%	35.40%	23.10%

INCOME TAXES - SCHEDULE OF DEFE

INCOME TAXES - SCHEDULE OF DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	(1.20%)	(32.80%)	(0.00%)
Deferred Income Tax Expense (Benefit)	$ 9,137	$ (50,396)	$ (45,174)
Deferred Tax Assets, Net [Abstract]
Accounts receivable	3,657	3,496
Employee benefits	20,107	14,835
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	12,840	16,341
Deferred Tax Assets, Tax Deferred Expense, Other	0	8,456
Tax loss carryforwards	15,557	19,128
Other	7,927	11,850
Deferred taxes, Assets	56,016	71,588
Deferred Tax Liabilities, Inventory	3,315	3,181
Deferred Tax Liabilities [Abstract]
Depreciation	17,384	13,283
Amortization of intangible assets	158,795	159,107
Other	4,115	8,672
Deferred Tax Assets, Gross	60,088	74,106
Deferred Tax Liabilities, Gross	183,609	184,243
Deferred Tax Assets, Valuation Allowance	$ (4,072)	(2,518)
Foreign Tax Authority
Deferred Tax Liabilities [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards		17,800
Foreign Tax Authority | Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2019
Foreign Tax Authority | Maximum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2028
State and Local Jurisdiction [Member]
Deferred Tax Assets, Net [Abstract]
Tax loss carryforwards	$ 3,200	$ 3,100
State and Local Jurisdiction [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2022
State and Local Jurisdiction [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2037

INCOME TAXES - NOLS (Details)

INCOME TAXES - NOLS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	$ 15,557	$ 19,128
Canada Revenue Agency [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	6,400	10,400
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	3,200	3,100
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	7,200	7,000
Operating Loss Carryforwards, Valuation Allowance	$ 4,100	$ 2,500
Minimum | Canada Revenue Agency [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2036
Minimum | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2022
Minimum | Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2019
Maximum | Canada Revenue Agency [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2037
Maximum | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 1, 2037
Maximum | Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2028

INCOME TAXES - SCHEDULE OF IN_2

INCOME TAXES - SCHEDULE OF INCOME TAX CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 1,300	$ 1,700	$ 7,500
Deferred Tax Assets, Tax Deferred Expense, Other	0	8,456
Unrecognized Tax Benefits, Interest on Income Taxes Expense	(200)	(100)	(1,200)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance January 1	4,348	6,181	5,436
Additions for tax positions of prior years	0	0	3,298
Reductions for tax positions of prior years	0	(155)	(21)
Settlements	(2,646)	(1,025)	(1,921)
Lapse in statute of limitations	(287)	(755)	(728)
Ending balance December 31	1,293	4,348	6,181
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation	$ (122)	$ (102)	$ (117)

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			36 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2014
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock									$ 127,169	$ 106,792	$ 4,818
Stock Repurchase Program, Authorized Amount	$ 400,000				$ 300,000				$ 400,000	$ 300,000		$ 300,000	$ 300,000
Stock Repurchase Program Expiration Date									Dec. 31, 2020	Dec. 31, 2017
Treasury Stock, Shares, Acquired									2,003,446	1,778,537
Net Income	$ 58,133	$ 66,849	$ 57,940	$ 44,421	$ 22,546	$ 53,675	$ 49,510	$ 37,729	$ 227,343	$ 163,460	$ 101,588
Weighted average common shares outstanding used in computing basic earnings per share									46,722,000	47,849,000	44,116,000
Common shares issuable upon exercise of dilutive stock options									477,000	512,000	543,000
Common shares issuable from contingently convertible debentures									0	0	3,674,000
Weighted average common shares outstanding and common share equivalents used in computing diluted earnings per share									47,199,000	48,361,000	48,333,000
Earnings Per Share attributable to WESCO International, Inc.
Basic	$ 1.27	$ 1.42	$ 1.23	$ 0.94	$ 0.48	$ 1.13	$ 1.03	$ 0.77	$ 4.87	$ 3.42	$ 2.30
Diluted	$ 1.26	$ 1.41	$ 1.22	$ 0.93	$ 0.47	$ 1.12	$ 1.02	$ 0.76	$ 4.82	$ 3.38	$ 2.10
Treasury Stock, Common [Member]
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock									$ 125,000	$ 100,000		$ 250,000
Treasury Stock, Common, Shares					4,247,113					4,247,113		4,247,113
Treasury Stock, Shares, Acquired									2,003,446	1,778,537

EARNINGS PER SHARE - EARNINGS P

EARNINGS PER SHARE - EARNINGS PER SHARE (Details) - USD ($)	12 Months Ended			36 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Payments for Repurchase of Common Stock	$ 127,169,000	$ 106,792,000	$ 4,818,000
Treasury Stock, Shares, Acquired	2,003,446	1,778,537
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	0	0	3,674,000
Stock Appreciation Rights (SARs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share	1,600,000	1,300,000	1,200,000
Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt Instrument, Convertible, Conversion Price	$ 28.87
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	11,951,932
Dilutive Securities, Effect on Basic Earnings Per Share			$ 0.17
Treasury Stock, Common [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Treasury Stock, Common, Shares		4,247,113		4,247,113
Payments for Repurchase of Common Stock	$ 125,000,000	$ 100,000,000		$ 250,000,000
Treasury Stock, Shares, Acquired	2,003,446	1,778,537

Textuals (Details)

Textuals (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Service Cost	$ 5,242	$ 4,328	$ 3,845
Defined contribution plan, employer discretionary contribution amount	20,600	10,000
Defined contribution plan, cost recognized	42,000	31,300	18,500
Deferred Compensation Liability, Classified, Noncurrent	$ 21,900	$ 24,300
Defined Benefit Plan, Description	The Company sponsors a contributory defined benefit plan (the "Plan") covering substantially all Canadian employees of EECOL. The Plan provides retirement benefits based on earnings and credited service, and participants contribute 2% of their earnings to the Plan. Participants become 100% vested after two years of continuous service or, if earlier, at the participant's normal retirement age.
Defined Benefit Plan, Unfunded Plan	The Company also sponsors a Supplemental Executive Retirement Plan (the "SERP"), which provides additional pension benefits to certain executives of EECOL based on earnings, and credited service. Effective January 1, 2013, the SERP was closed to new participants and existing participants became 100% vested. SERP participants continue to contribute 4% of their earnings to the Plan.
Pension Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.00%	3.50%
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 2,900
Other Nonoperating Gains (Losses)	$ (1,900)	$ (1,800)	$ (1,500)
Supplemental Employee Retirement Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.00%	3.50%
Other Postretirement Benefits Plan [Member]
Schedule of Employee Benefit Plans [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 400
United States
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	50.00%
Defined contribution plan, maximum annual contribution per employee, percent	6.00%
Canada | Minimum
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	3.00%
Canada | Maximum
Schedule of Employee Benefit Plans [Line Items]
Defined contribution plan, employer matching contribution, percent	5.00%

EMPLOYEE BENEFIT PLANS Benefit

EMPLOYEE BENEFIT PLANS Benefit Obligations, Plan Assets, and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Accumulated Benefit Obligation (ABO) at December 31	$ 78,746	$ 92,375
PBO at beginning of year	120,319	96,160
Service cost	5,242	4,328	$ 3,845
Interest cost	4,137	3,912	3,856
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	745	735
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	5,969	5,562	5,328
Defined Benefit Plan, Amortization of Gain (Loss)	$ 46	$ 149	31
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan [Table Text Block]	(11,643.715)	10,906
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ 3,892	$ 3,005
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	46	149	31
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	(5,204)	8,742	2,787
PBO at end of year	105,515	120,319	96,160
Plan assets at beginning of year	97,182	84,753
Actual return on plan assets	(425)	7,875
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	745	735
Company contributions	372	368
Defined Benefit Plan, Plan Assets, Benefits Paid	3,892	3,005
Plan assets at end of year	86,556	97,182	$ 84,753
Funded status	(18,959)	(23,137)
Current liabilities	(364)	(395)
Non-current liabilities	(18,595)	(22,742)
Net pension liability at end of year	(18,959)	(23,137)
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	(2,696)	2,508
Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss)	(9,392)	7,283
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)	(7,426)	6,456
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	$ (2,696)	$ 2,508

EMPLOYEE BENEFIT PLANS Pension

EMPLOYEE BENEFIT PLANS Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefit Expense	$ (434)	$ 8,910	$ 4,827
Service cost	5,242	4,328	3,845
Interest cost	4,137	3,912	3,856
Expected return on plan assets	(5,969)	(5,562)	(5,328)
Defined Benefit Plan, Amortization of Gain (Loss)	(46)	(149)	(31)
Total net periodic pension cost	3,364	2,529	2,342
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(5,250)	8,593	2,756
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	46	149	31
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	(5,204)	8,742	2,787
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	1,406	(2,361)	(302)
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	$ (3,798)	$ 6,381	$ 2,485

EMPLOYEE BENEFIT PLANS Assumpti

EMPLOYEE BENEFIT PLANS Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.75%	3.75%	4.00%
Discount rate	4.00%	3.50%
Average salary increases	3.80%	3.80%
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.75%	3.75%	4.00%
Discount rate	4.00%	3.50%
Average salary increases	3.80%	3.80%

EMPLOYEE BENEFIT PLANS Assump_2

EMPLOYEE BENEFIT PLANS Assumptions 2 (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.00%	3.50%
Discount rate	3.50%	3.90%	4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.40%	6.40%	6.40%
Rate of compensation increase	3.75%	3.75%	4.00%
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.00%	3.50%
Discount rate	3.50%	3.90%	4.20%
Rate of compensation increase	3.75%	3.75%	4.00%

EMPLOYEE BENEFIT PLANS Benefi_2

EMPLOYEE BENEFIT PLANS Benefit payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Retirement Benefits [Abstract]
2,013	$ 2,870
2,014	2,946
2,015	3,098
2,016	3,196
2,017	3,448
2018-2023	$ 21,721

EMPLOYEE BENEFIT PLANS Asset al

EMPLOYEE BENEFIT PLANS Asset allocations (Details)	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure
Equity securities	100.00%	100.00%
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Equity securities	44.70%	41.40%
Other Investments [Member]
Defined Benefit Plan Disclosure
Equity securities	15.40%	21.70%
Canada | Equity Securities [Member]
Defined Benefit Plan Disclosure
Equity securities	12.40%	11.50%
United States | Equity Securities [Member]
Defined Benefit Plan Disclosure
Equity securities	5.00%	4.60%
Non-US [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure
Equity securities	22.50%	20.80%

EMPLOYEE BENEFIT PLANS Target a

EMPLOYEE BENEFIT PLANS Target asset allocation (Details)	12 Months Ended
	Dec. 31, 2018
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description	The primary investment objective, in support of the overall objective, is to earn the highest rate of return possible for the Plan, while keeping risk at acceptable levels. The long-term return objective of the Plan is to achieve a minimum annualized rate of return in excess of the actuarial requirements. This translates into a required return of 3.0% above inflation, net of investment management fees. The return objective is consistent with the overall investment risk level that the Plan assumes in order to meet the pension obligations of the Plan. To achieve this long term investment objective, the Plan has adopted an asset mix that has a combination of primarily equity and fixed income investments. Risk is controlled by investing in a well-diversified portfolio of asset classes. A benchmark portfolio is established based on the expected returns for each asset class available. The investment of the Plan's assets in accordance with the benchmark portfolio should enable the Plan to not only attain, but also exceed the minimum overall objective.
Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	40.00%
Fixed Income Funds [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	45.00%
Other Investments [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	15.00%
United States | Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	27.50%
Canada | Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities	12.50%

EMPLOYEE BENEFIT PLANS Fair val

EMPLOYEE BENEFIT PLANS Fair value plan assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure
Total investments	100.00%	100.00%
Defined Benefit Plan, Plan Assets, Amount	$ 86,556	$ 97,182	$ 84,753
Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	203	3,996
Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Total investments	44.70%	41.40%
Defined Benefit Plan, Plan Assets, Amount	$ 38,668	$ 40,193
Fixed Income Investments [Member] | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Fixed Income Investments [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Fixed Income Investments [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Other Investments [Member]
Defined Benefit Plan Disclosure
Total investments	15.40%	21.70%
Defined Benefit Plan, Plan Assets, Amount	$ 13,347	$ 21,135
Other Investments [Member] | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	203	3,996
Other Investments [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Other Investments [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Canada | Equity Securities [Member]
Defined Benefit Plan Disclosure
Total investments	12.40%	11.50%
Defined Benefit Plan, Plan Assets, Amount	$ 10,693	$ 11,211
Canada | Equity Securities [Member] | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Canada | Equity Securities [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Canada | Equity Securities [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
United States | Equity Securities [Member]
Defined Benefit Plan Disclosure
Total investments	5.00%	4.60%
Defined Benefit Plan, Plan Assets, Amount	$ 4,356	$ 4,436
United States | Equity Securities [Member] | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
United States | Equity Securities [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
United States | Equity Securities [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0
Non-US [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure
Total investments	22.50%	20.80%
Defined Benefit Plan, Plan Assets, Amount	$ 19,492	$ 20,207
Non-US [Member] | Equity Securities [Member] | Level 1
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Non-US [Member] | Equity Securities [Member] | Level 2
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Non-US [Member] | Equity Securities [Member] | Level 3
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	0	0
Estimate of Fair Value Measurement [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	86,353	93,186
Estimate of Fair Value Measurement [Member] | Fixed Income Investments [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	38,668	40,193
Estimate of Fair Value Measurement [Member] | Other Investments [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	13,144	17,139
Estimate of Fair Value Measurement [Member] | Canada | Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	10,693	11,211
Estimate of Fair Value Measurement [Member] | United States | Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	4,356	4,436
Estimate of Fair Value Measurement [Member] | Non-US [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure
Defined Benefit Plan, Plan Assets, Amount	$ 19,492	$ 20,207

STOCK-BASED COMPENSATION - STOC

STOCK-BASED COMPENSATION - STOCK-BASED COMPENSATION (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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				$ 16,445	$ 14,809	$ 12,493
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value				$ 8,200	17,200	13,000
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				3,100,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 18,800
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense				$ 2,000	$ 6,400	$ 4,900
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				$ 18.38	$ 20.52	$ 12.88
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				327,798	290,054	257,096	175,411
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value				$ 62.40	$ 71.33	$ 44.45
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 16,400	$ 14,800	$ 12,500
Scenario, Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 800	$ 6,300	$ 11,700
Share-based Compensation Award, 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				48,098

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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	$ 40.74	$ 42.19	$ 41.54
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	138,896	148,508	149,320	114,520
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 62.80	$ 76.63	$ 47
Share Based Compensation Arrangements By Share Based Payment Award, Options and Stock Appreciation Rights Outstanding [Roll Forward]
Stock-settled appreciation rights granted	44,144	39,978	91,768
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	$ 18.38	$ 20.52	$ 12.88
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	192,700	495,181	526,818
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures	203,320	161,506	310,715
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 68.69	$ 66.06	$ 63.71
Weighted Average Remaining Contractual Term, Outstanding	6 years 1 month
Weighted Average Remaining Contractual Term, Exercisable	4 years 7 months
Aggregate Intrinsic Value, Outstanding	$ 6,514
Aggregate Intrinsic Value, Exercisable	$ 5,623
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	1,453,932	1,331,580	1,549,350
Stock-settled appreciation rights granted	509,046	455,807	709,999
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 57.93	$ 56.96	$ 53.35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 59.26	$ 57.75	$ 52.62	$ 54.47
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	2,351,633	2,238,607	2,439,487	2,567,021
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 62.68	$ 71.21	$ 42.63
Share-based Compensation Award, 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	90,798
Share-based Compensation Award, 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	48,098

STOCK-BASED COMPENSATION - SUMM

STOCK-BASED COMPENSATION - SUMMARY OF RESTRICTED STOCK UNITS AND PERFORMANCE-BASED AWARDS (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	138,896	148,508	149,320	114,520
Granted	44,144	39,978	91,768
Vested in Period	0	0	0
Forfeited in Period	(53,756)	(40,790)	(56,968)
Unvested, Weighted Average Fair Value	$ 59.33	$ 60.23	$ 60.36	$ 76.48
Granted, Weighted Average Fair Value	62.80	76.63	47
Vested in Period, Weighted Average Fair Value	0	0	0
Forfeited in Period, Weighted Average Fair Value	$ 64.67	$ 76.77	$ 71.25
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	327,798	290,054	257,096	175,411
Granted	122,062	100,993	162,256
Vested in Period	(64,166)	(44,720)	(60,015)
Forfeited in Period	(20,152)	(23,315)	(20,556)
Unvested, Weighted Average Fair Value	$ 57.87	$ 58.11	$ 57.47	$ 74.52
Granted, Weighted Average Fair Value	62.40	71.33	44.45
Vested in Period, Weighted Average Fair Value	67.91	84.57	72.41
Forfeited in Period, Weighted Average Fair Value	$ 58.15	$ 57.52	$ 59.15
Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	48,098
Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	90,798
Share-based Compensation Award, 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	48,098
Share-based Compensation Award, 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	21,350
Share-based Compensation Award, Tranche Two [Member] | Return on Net Assets [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Unvested, Shares	21,350

STOCK-BASED COMPENSATION - SC_2

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED PAYMENT AWARDS, VALUATION ASSUMPTIONS (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	2.50%	1.90%	1.20%
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-settled appreciation rights granted	509,046	455,807	709,999
Expected life (in years)	5 years	5 years	5 years
Expected volatility	28.00%	29.00%	32.00%
Share-based Compensation Award, 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	48,098

STOCK-BASED COMPENSATION - SC_3

STOCK-BASED COMPENSATION - SCHEDULE OF SHARE-BASED PAYMENT AWARD, PERFORMANCE-BASED AWARDS, VALUATION ASSUMPTIONS (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.50%	1.90%	1.20%
Correlation		0.00%	0.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date share price	$ 62.80	$ 71.67	$ 42.44
WESCO expected volatility		0.00%	0.00%
Risk-free interest rate		0.00%	0.00%

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Operating Leases, Rent Expense	$ 86	$ 82	$ 76.7

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - SCHEDULE OF FUTURE MINIMUM RENTAL PAYMENTS (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due [Abstract]
2,013	$ 71,640
2,014	59,594
2,015	47,264
2,016	34,490
2,017	24,493
Thereafter	$ 40,302

SEGMENTS AND RELATED INFORMAT_3

SEGMENTS AND RELATED INFORMATION - SEGMENTS AND RELATED INFORMATION (Details)	Dec. 31, 2018stockkeepingunitsproducts
Segment Reporting [Abstract]
Product stock keeping units (in stock keeping units) | stockkeepingunits	220,000
Products (in products) | products	1,000,000

OTHER FINANCIAL INFORMATION - O

OTHER FINANCIAL INFORMATION - OTHER FINANCIAL INFORMATION (Details) - Unsecured Debt [Member] $ in Millions	Dec. 31, 2018USD ($)
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500
2024 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 350

OTHER FINANCIAL INFORMATION - C

OTHER FINANCIAL INFORMATION - CONDENSED CONSOLIDATED BALANCE SHEETS (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Information
Cash and cash equivalents	$ 96,343	$ 117,953	$ 110,131	$ 160,279
Trade accounts receivable	1,166,607	1,170,080
Inventories, net	948,726	956,148
Prepaid Expense and Other Assets, Current	52,107	40,189
Total current assets	2,385,640	2,408,849
Property, building and equipment, net	160,878	156,445
Intangible assets, net	316,016	367,104
Goodwill and other intangibles, net	1,722,603	1,771,877	1,730,950
Other assets	3,525	6,990
Total assets	4,605,036	4,735,468
Accounts payable	794,348	799,520
Short-term debt	30,785	34,075
Other Liabilities, Current	105,461	95,820
Total current liabilities	1,061,946	1,040,969
Long-term debt	1,167,311	1,313,261
Long-term Debt, Excluding Current Maturities	1,167,311	1,313,261
Total WESCO International stockholders' equity	2,129,726	2,116,143
Stockholders' Equity Attributable to Parent	2,135,310	2,119,739
Noncontrolling interest	(5,584)	(3,596)	(3,269)	(2,801)
Total liabilities and stockholders' equity	4,605,036	4,735,468
Parent Company
Condensed Financial Information
Cash and cash equivalents	0	0	0	0
Trade accounts receivable	0	0
Inventories, net	0	0
Prepaid Expense and Other Assets, Current	1,123	4,730
Total current assets	1,123	4,730
Intercompany receivables, net	0	0
Property, building and equipment, net	0	0
Intangible assets, net	0	0
Goodwill and other intangibles, net	0	0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	3,182,469	3,058,613
Other assets	0	0
Total assets	3,183,592	3,063,343
Accounts payable	0	0
Short-term debt	0	0
Other Liabilities, Current	0	0
Total current liabilities	0	0
Intercompany payables, net	1,048,282	939,784
Long-term Debt, Excluding Current Maturities	0	0
Liabilities, Other than Long-term Debt, Noncurrent	0	3,820
Stockholders' Equity Attributable to Parent	2,135,310	2,119,739
Noncontrolling interest	0	0
Total liabilities and stockholders' equity	3,183,592	3,063,343
Guarantor Subsidiaries
Condensed Financial Information
Cash and cash equivalents	35,931	50,602	41,552	38,963
Trade accounts receivable	0	0
Inventories, net	440,422	430,092
Prepaid Expense and Other Assets, Current	57,586	42,547
Total current assets	533,939	523,241
Intercompany receivables, net	0	0
Property, building and equipment, net	63,506	50,198
Intangible assets, net	2,131	2,770
Goodwill and other intangibles, net	257,623	257,623
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	5,137,783	5,023,826
Other assets	2,905	2,778
Total assets	5,997,887	5,860,436
Accounts payable	404,373	417,690
Short-term debt	0	0
Other Liabilities, Current	86,600	80,039
Total current liabilities	490,973	497,729
Intercompany payables, net	1,355,422	1,249,352
Long-term Debt, Excluding Current Maturities	842,093	934,033
Liabilities, Other than Long-term Debt, Noncurrent	126,930	120,709
Stockholders' Equity Attributable to Parent	3,182,469	3,058,613
Noncontrolling interest	0	0
Total liabilities and stockholders' equity	5,997,887	5,860,436
Non-Guarantor Subsidiaries
Condensed Financial Information
Cash and cash equivalents	60,412	67,351	68,579	121,316
Trade accounts receivable	1,166,607	1,170,080
Inventories, net	508,304	526,056
Prepaid Expense and Other Assets, Current	124,523	152,531
Total current assets	1,859,846	1,916,018
Intercompany receivables, net	2,403,704	2,189,136
Property, building and equipment, net	97,372	106,247
Intangible assets, net	313,885	364,334
Goodwill and other intangibles, net	1,464,980	1,514,254
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures		0
Other assets	16,994	28,415
Total assets	6,156,781	6,118,404
Accounts payable	389,975	381,830
Short-term debt	30,785	34,075
Other Liabilities, Current	159,481	162,475
Total current liabilities	580,241	578,380
Intercompany payables, net	0	0
Long-term Debt, Excluding Current Maturities	325,218	379,228
Liabilities, Other than Long-term Debt, Noncurrent	119,123	140,566
Stockholders' Equity Attributable to Parent	5,137,783	5,023,826
Noncontrolling interest	(5,584)	(3,596)
Total liabilities and stockholders' equity	6,156,781	6,118,404
Consolidated Entities [Member]
Condensed Financial Information
Cash and cash equivalents	96,343	117,953	110,131	160,279
Trade accounts receivable	1,166,607	1,170,080
Inventories, net	948,726	956,148
Prepaid Expense and Other Assets, Current	173,964	164,668
Total current assets	2,385,640	2,408,849
Intercompany receivables, net	0	0
Property, building and equipment, net	160,878	156,445
Intangible assets, net	316,016	367,104
Goodwill and other intangibles, net	1,722,603	1,771,877
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0	0
Other assets	19,899	31,193
Total assets	4,605,036	4,735,468
Accounts payable	794,348	799,520
Short-term debt	30,785	34,075
Other Liabilities, Current	236,813	207,374
Total current liabilities	1,061,946	1,040,969
Intercompany payables, net	0	0
Long-term Debt, Excluding Current Maturities	1,167,311	1,313,261
Liabilities, Other than Long-term Debt, Noncurrent	246,053	265,095
Stockholders' Equity Attributable to Parent	2,135,310	2,119,739
Noncontrolling interest	(5,584)	(3,596)
Total liabilities and stockholders' equity	4,605,036	4,735,468
Consolidation, Eliminations
Condensed Financial Information
Cash and cash equivalents	0	0	$ 0	$ 0
Trade accounts receivable	0	0
Inventories, net	0	0
Prepaid Expense and Other Assets, Current	(9,268)	(35,140)
Total current assets	(9,268)	(35,140)
Intercompany receivables, net	(2,403,704)	(2,189,136)
Property, building and equipment, net	0	0
Intangible assets, net	0	0
Goodwill and other intangibles, net	0	0
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(8,320,252)	(8,082,439)
Other assets		0
Total assets	(10,733,224)	(10,306,715)
Accounts payable	0	0
Short-term debt	0	0
Other Liabilities, Current	(9,268)	(35,140)
Total current liabilities	(9,268)	(35,140)
Intercompany payables, net	(2,403,704)	(2,189,136)
Long-term Debt, Excluding Current Maturities	0	0
Liabilities, Other than Long-term Debt, Noncurrent	0	0
Stockholders' Equity Attributable to Parent	(8,320,252)	(8,082,439)
Noncontrolling interest	0	0
Total liabilities and stockholders' equity	$ (10,733,224)	$ (10,306,715)

OTHER FINANCIAL INFORMATION -_2

OTHER FINANCIAL INFORMATION - CONDENSED CONSOLIDATED INCOME STATEMENT (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Information
Revenues	$ 2,011,447	$ 2,067,245	$ 2,103,994	$ 1,993,915	$ 1,996,647	$ 2,000,159	$ 1,909,624	$ 1,772,591	$ 8,176,601	$ 7,679,021	$ 7,336,017
Cost of goods sold	1,621,117	1,670,037	1,704,100	1,613,966	1,613,469	1,614,814	1,543,510	1,422,573	6,609,220	6,194,366	5,887,814
Selling, General and Administrative Expense									(1,151,944)	(1,101,598)	(1,050,799)
Depreciation, Depletion and Amortization, Nonproduction									(62,997)	(64,017)	(66,858)
Other Nonoperating Income (Expense)									(71,415)	(66,600)	(75,062)
Loss on debt extinguishment									0	0	123,933
Income tax expense									55,670	89,307	30,431
Net income	58,066	66,645	57,673	42,971	22,222	53,576	49,535	37,800	225,355	163,133	101,120
Net Income (Loss) Attributable to Noncontrolling Interest									(1,988)	(327)	(468)
Net Income	$ 58,133	$ 66,849	$ 57,940	$ 44,421	$ 22,546	$ 53,675	$ 49,510	$ 37,729	227,343	163,460	101,588
Foreign currency translation adjustment									(99,643)	85,762	38,275
Benefit plan adjustments									3,798	(6,381)	(2,485)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									131,498	242,841	137,378
Parent Company
Condensed Financial Information
Revenues									0	0	0
Cost of goods sold									0	0	0
Selling, General and Administrative Expense									0	0	(61)
Depreciation, Depletion and Amortization, Nonproduction									0	0	0
Income (Loss) from Subsidiaries, before Tax									225,355	160,587	240,571
Interest Income (Expense), Net											(17,555)
Other Nonoperating Income (Expense)									0	0
Loss on debt extinguishment											(123,933)
Income tax expense									0	(2,546)	(2,098)
Net income									225,355	163,133	101,120
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income									225,355	163,133	101,120
Foreign currency translation adjustment									(99,643)	85,762	38,275
Benefit plan adjustments									3,798	(6,381)	(2,485)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									129,510	242,514	136,910
Consolidation, Eliminations [Member]
Condensed Financial Information
Loss on debt extinguishment											0
Guarantor Subsidiaries
Condensed Financial Information
Revenues									3,572,406	3,370,088	3,306,265
Cost of goods sold									2,890,490	2,714,511	2,651,409
Selling, General and Administrative Expense									(590,009)	(555,503)	(477,437)
Depreciation, Depletion and Amortization, Nonproduction									(18,334)	(18,442)	(20,226)
Income (Loss) from Subsidiaries, before Tax									209,802	168,782	155,814
Interest Income (Expense), Net											(87,824)
Other Nonoperating Income (Expense)									(54,178)	(94,313)
Loss on debt extinguishment											0
Income tax expense									3,842	(4,486)	8,263
Net income									225,355	160,587	216,920
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income									225,355	160,587	216,920
Foreign currency translation adjustment									(99,643)	85,762	38,275
Benefit plan adjustments									3,798	(6,381)	(2,485)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									129,510	239,968	252,710
Non-Guarantor Subsidiaries
Condensed Financial Information
Revenues									4,757,321	4,441,655	4,134,508
Cost of goods sold									3,871,856	3,612,577	3,341,161
Selling, General and Administrative Expense									(561,935)	(546,095)	(573,301)
Depreciation, Depletion and Amortization, Nonproduction									(44,663)	(45,575)	(46,632)
Income (Loss) from Subsidiaries, before Tax									0	0	0
Interest Income (Expense), Net											30,317
Other Nonoperating Income (Expense)									(17,237)	27,713
Loss on debt extinguishment											0
Income tax expense									51,828	96,339	24,266
Net income									209,802	168,782	179,465
Net Income (Loss) Attributable to Noncontrolling Interest									(1,988)	(327)	(468)
Net Income									211,790	169,109	179,933
Foreign currency translation adjustment									(99,643)	85,762	38,275
Benefit plan adjustments									3,798	(6,381)	(2,485)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									115,945	248,490	215,723
Consolidated Entities [Member]
Condensed Financial Information
Revenues									8,176,601	7,679,021	7,336,017
Cost of goods sold									6,609,220	6,194,366	5,887,814
Selling, General and Administrative Expense									(1,151,944)	(1,101,598)	(1,050,799)
Depreciation, Depletion and Amortization, Nonproduction									(62,997)	(64,017)	(66,858)
Income (Loss) from Subsidiaries, before Tax									0	0	0
Interest Income (Expense), Net											(75,062)
Other Nonoperating Income (Expense)									(71,415)	(66,600)
Loss on debt extinguishment											(123,933)
Income tax expense									55,670	89,307	30,431
Net income									225,355	163,133	101,120
Net Income (Loss) Attributable to Noncontrolling Interest									(1,988)	(327)	(468)
Net Income									227,343	163,460	101,588
Foreign currency translation adjustment									(99,643)	85,762	38,275
Benefit plan adjustments									3,798	(6,381)	(2,485)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									131,498	242,841	137,378
Consolidation, Eliminations [Member]
Condensed Financial Information
Revenues									(153,126)	(132,722)	(104,756)
Cost of goods sold									(153,126)	(132,722)	(104,756)
Selling, General and Administrative Expense									0	0	0
Depreciation, Depletion and Amortization, Nonproduction									0	0	0
Income (Loss) from Subsidiaries, before Tax									(435,157)	(329,369)	(396,385)
Interest Income (Expense), Net											0
Other Nonoperating Income (Expense)									0	0
Income tax expense									0	0	0
Net income									(435,157)	(329,369)	(396,385)
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income									(435,157)	(329,369)	(396,385)
Foreign currency translation adjustment									199,286	(171,524)	(76,550)
Benefit plan adjustments									(7,596)	12,762	4,970
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(243,467)	(488,131)	(467,965)
Pension Plan [Member]
Condensed Financial Information
Other Nonoperating Gains (Losses)									$ (1,900)	$ (1,800)	$ (1,500)

OTHER FINANCIAL INFORMATION -_3

OTHER FINANCIAL INFORMATION - CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Information
Net cash (used) provided by operating activities	$ 296,721	$ 149,122	$ 300,235
Investing Activities:
Capital expenditures	(36,210)	(21,507)	(17,957)
Payments to Acquire Businesses, Net of Cash Acquired	0	0	(50,890)
Proceeds from sale of assets	12,461	6,766	8,361
Advances to subsidiaries and other	(10,393)	9,446	(10,000)
Net cash used in investing activities	(34,142)	(5,295)	(70,486)
Financing Activities:
Other	(1,211)	(1,477)	337
Net cash provided (used) by financing activities	(275,094)	(141,196)	(276,263)
Effect of exchange rate changes on cash and cash equivalents	(9,095)	5,191	(3,634)
Net change in cash and cash equivalents	(21,610)	7,822	(50,148)
Cash and cash equivalents at the beginning of period	117,953	110,131	160,279
Cash and cash equivalents at the end of period	96,343	117,953	110,131
Parent Company
Condensed Financial Information
Net cash (used) provided by operating activities	18,672	(36,575)	95,388
Investing Activities:
Capital expenditures	0	0	0
Payments to Acquire Businesses, Net of Cash Acquired			0
Proceeds from sale of assets	0	0	0
Proceeds from Dividends Received		0	0
Payments for Advance to Affiliate	0	0	0
Net cash used in investing activities	0	0	0
Financing Activities:
Proceeds from Issuance of Debt	108,497	143,367	252,246
Repayments of Debt	0	0	(344,804)
Equity transactions	(127,169)	(106,792)	(2,830)
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees		0	0
Other	0	0	0
Net cash provided (used) by financing activities	(18,672)	36,575	(95,388)
Effect of exchange rate changes on cash and cash equivalents		0	0
Net change in cash and cash equivalents	0	0	0
Cash and cash equivalents at the beginning of period	0	0	0
Cash and cash equivalents at the end of period	0	0	0
Guarantor Subsidiaries
Condensed Financial Information
Net cash (used) provided by operating activities	153,467	101,826	(243,476)
Investing Activities:
Capital expenditures	(17,573)	(13,215)	(12,482)
Payments to Acquire Businesses, Net of Cash Acquired			(50,890)
Proceeds from sale of assets	0	0	0
Proceeds from Dividends Received	347,531	307,784	82,912
Payments for Advance to Affiliate	406,028	383,686	297,259
Net cash used in investing activities	(76,070)	(89,117)	(277,719)
Financing Activities:
Proceeds from Issuance of Debt	339,606	775,926	1,566,864
Repayments of Debt	(410,606)	(785,392)	(1,030,520)
Equity transactions	0	0	0
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees		0	0
Other	(21,068)	5,807	(12,560)
Net cash provided (used) by financing activities	(92,068)	(3,659)	523,784
Effect of exchange rate changes on cash and cash equivalents		0	0
Net change in cash and cash equivalents	(14,671)	9,050	2,589
Cash and cash equivalents at the beginning of period	50,602	41,552	38,963
Cash and cash equivalents at the end of period	35,931	50,602	41,552
Non-Guarantor Subsidiaries
Condensed Financial Information
Net cash (used) provided by operating activities	124,582	83,871	448,323
Investing Activities:
Capital expenditures	(18,637)	(8,292)	(5,475)
Payments to Acquire Businesses, Net of Cash Acquired			0
Proceeds from sale of assets	12,461	6,766	8,361
Proceeds from Dividends Received		0	0
Payments for Advance to Affiliate	(196,219)	(26,912)	337,344
Net cash used in investing activities	190,043	25,386	(334,458)
Financing Activities:
Proceeds from Issuance of Debt	1,086,673	1,144,848	672,345
Repayments of Debt	(1,051,611)	(952,740)	(752,401)
Equity transactions	0	0	0
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	(347,531)	(307,784)	(82,912)
Other	0	0	0
Net cash provided (used) by financing activities	(312,469)	(115,676)	(162,968)
Effect of exchange rate changes on cash and cash equivalents	(9,095)	5,191	(3,634)
Net change in cash and cash equivalents	(6,939)	(1,228)	(52,737)
Cash and cash equivalents at the beginning of period	67,351	68,579	121,316
Cash and cash equivalents at the end of period	60,412	67,351	68,579
Consolidated Entities [Member]
Condensed Financial Information
Net cash (used) provided by operating activities	296,721	149,122	300,235
Investing Activities:
Capital expenditures	(36,210)	(21,507)	(17,957)
Payments to Acquire Businesses, Net of Cash Acquired			(50,890)
Proceeds from sale of assets	12,461	6,766	8,361
Proceeds from Dividends Received	0	0	0
Payments for Advance to Affiliate	10,393	(9,446)	10,000
Net cash used in investing activities	(34,142)	(5,295)	(70,486)
Financing Activities:
Proceeds from Issuance of Debt	1,335,360	1,680,455	2,194,196
Repayments of Debt	(1,462,217)	(1,720,666)	(2,455,069)
Equity transactions	(127,169)	(106,792)	(2,830)
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	0	0	0
Other	(21,068)	5,807	(12,560)
Net cash provided (used) by financing activities	(275,094)	(141,196)	(276,263)
Effect of exchange rate changes on cash and cash equivalents	(9,095)	5,191	(3,634)
Net change in cash and cash equivalents	(21,610)	7,822	(50,148)
Cash and cash equivalents at the beginning of period	117,953	110,131	160,279
Cash and cash equivalents at the end of period	96,343	117,953	110,131
Consolidation, Eliminations
Condensed Financial Information
Net cash (used) provided by operating activities	0	0	0
Investing Activities:
Capital expenditures	0	0	0
Payments to Acquire Businesses, Net of Cash Acquired			0
Proceeds from sale of assets	0	0	0
Proceeds from Dividends Received	(347,531)	(307,784)	(82,912)
Payments for Advance to Affiliate	(199,416)	(366,220)	(624,603)
Net cash used in investing activities	(148,115)	58,436	541,691
Financing Activities:
Proceeds from Issuance of Debt	(199,416)	(383,686)	(297,259)
Repayments of Debt	0	17,466	(327,344)
Equity transactions	0	0	0
SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Subsidiaries and Equity Method Investees	347,531	307,784	82,912
Other	0	0	0
Net cash provided (used) by financing activities	148,115	(58,436)	(541,691)
Effect of exchange rate changes on cash and cash equivalents	0	0	0
Net change in cash and cash equivalents	0	0	0
Cash and cash equivalents at the beginning of period	0	0	0
Cash and cash equivalents at the end of period	$ 0	$ 0	$ 0

SELECTED QUARTERLY FINANCIAL _3

SELECTED QUARTERLY FINANCIAL DATA (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Gain (Loss) on Extinguishment of Debt									$ 0	$ 0	$ (123,933)
Revenues	$ 2,011,447	$ 2,067,245	$ 2,103,994	$ 1,993,915	$ 1,996,647	$ 2,000,159	$ 1,909,624	$ 1,772,591	8,176,601	7,679,021	7,336,017
Cost of goods sold	1,621,117	1,670,037	1,704,100	1,613,966	1,613,469	1,614,814	1,543,510	1,422,573	6,609,220	6,194,366	5,887,814
Income from operations	90,499	97,517	91,183	73,241	81,446	89,250	83,105	67,089	352,440	319,040	330,546
Income before income taxes	73,658	80,467	73,442	53,458	63,844	71,939	66,289	50,368	281,025	252,440	131,551
Net income	58,066	66,645	57,673	42,971	22,222	53,576	49,535	37,800	225,355	163,133	101,120
Net Income attributable to WESCO International, Inc.	$ 58,133	$ 66,849	$ 57,940	$ 44,421	$ 22,546	$ 53,675	$ 49,510	$ 37,729	$ 227,343	$ 163,460	$ 101,588
Basic earnings per share attributable to WESCO International, Inc.	$ 1.27	$ 1.42	$ 1.23	$ 0.94	$ 0.48	$ 1.13	$ 1.03	$ 0.77	$ 4.87	$ 3.42	$ 2.30
Diluted earnings per share attributable to WESCO International, Inc.	$ 1.26	$ 1.41	$ 1.22	$ 0.93	$ 0.47	$ 1.12	$ 1.02	$ 0.76	$ 4.82	$ 3.38	$ 2.10

Schedule II - Valuation and Q_3

Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount		$ 24,468	$ 21,313	$ 22,007	$ 22,587
Valuation Allowances and Reserves, Charged to Cost and Expense		10,854	8,466	5,888
Valuation Allowances and Reserves, Charged to Other Accounts		0	0	21
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	[1]	$ (7,699)	$ (9,160)	$ (6,489)
[1]	(1) Represents allowance for doubtful accounts in connection with certain acquisitions and divestitures.

REVENUE (Details)

REVENUE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 8,176,601	$ 7,679,021	$ 7,336,017
Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,983,062	2,852,357	2,644,442
Construction [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,684,844	2,546,261	2,482,624
Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,303,697	1,181,704	1,158,651
Commercial, Institutional and Government [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,204,998	1,098,699	1,050,300
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	6,089,130	5,775,988	5,635,803
Non-US [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,087,471	$ 1,903,033	$ 1,700,214

REVENUE Service Revenue (Detail

REVENUE Service Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 8,176,601	$ 7,679,021	$ 7,336,017

REVENUE Shipping and Handling_2

REVENUE Shipping and Handling (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									$ 8,176,601	$ 7,679,021	$ 7,336,017
Cost of Goods and Services Sold	$ 1,621,117	$ 1,670,037	$ 1,704,100	$ 1,613,966	$ 1,613,469	$ 1,614,814	$ 1,543,510	$ 1,422,573	6,609,220	6,194,366	5,887,814
Service [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									23,300	26,200	27,100
Shipping and Handling [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									$ 74,100	$ 61,800	$ 57,900

Deferred Revenue (Details)

Deferred Revenue (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Deferred Revenue	$ 11.8	$ 15.5