EARNINGS PER SHARE - SCHEDULE OF EARNINGS PER SHARE, BASIC AND DILUTED (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock									$ 2,901	$ 153,049	$ 127,169
Stock Repurchase Program, Authorized Amount	$ 400,000				$ 300,000				$ 400,000	$ 300,000	$ 300,000
Stock Repurchase Program Expiration Date									Dec. 31, 2020
Treasury Stock, Shares, Acquired										3,455,584	2,003,446
Preferred Stock Dividends, Income Statement Impact									$ 30,139	$ 0	$ 0
Weighted average common shares outstanding used in computing basic earnings per share									46,174,000	43,104,000	46,722,000
Common shares issuable upon exercise of dilutive stock options									451,000	383,000	477,000
Weighted average common shares outstanding and common share equivalents used in computing diluted earnings per share									46,625,000	43,487,000	47,199,000
Earnings Per Share attributable to WESCO International, Inc.
Basic	$ 0.11	$ 1.32	$ (0.84)	$ 0.82	$ 1.27	$ 1.53	$ 1.46	$ 0.94	$ 1.53	$ 5.18	$ 4.87
Diluted	$ 0.11	$ 1.31	$ (0.84)	$ 0.82	$ 1.26	$ 1.52	$ 1.45	$ 0.93	$ 1.51	$ 5.14	$ 4.82
Net Income (Loss) Available to Common Stockholders, Basic	$ 5,632	$ 66,167	$ (35,782)	$ 34,407	$ 53,098	$ 64,495	$ 63,464	$ 42,369	$ 70,421	$ 223,426	$ 227,343
Net Income attributable to WESCO International, Inc.									100,560	223,426	$ 227,343
Treasury Stock, Common [Member]
Accelerated Share Repurchases [Line Items]
Payments for Repurchase of Common Stock			$ 150,000						$ 275,000	$ 125,000
Treasury Stock, Common, Shares	5,459,030			365,272					5,459,030
Treasury Stock, Shares, Acquired									3,090,312	2,368,738