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