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