ACQUISITIONS (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) countries numberOfCities	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) countries numberOfCities	Jun. 30, 2020 USD ($)	Jun. 22, 2020 USD ($) $ / shares shares
Business Acquisition [Line Items]
Number of Cities in which an Entity Operates | numberOfCities	300		300
Revenue from Contract with Customer, Excluding Assessed Tax	$ 4,595,790,000	$ 2,086,706,000	$ 8,637,267,000	$ 4,055,353,000
Operating Income (Loss)	218,872,000	15,270,000	352,123,000	76,183,000
Revenues	$ 4,595,790,000	2,086,706,000	$ 8,637,267,000	4,055,353,000
Business Combination, Goodwill Recognized, Description			The resulting goodwill is primarily attributable to Anixter's workforce, significant cross-selling opportunities in additional geographies, enhanced scale, and other operational efficiencies.During the second quarter of 2021, the Company finalized its allocation of the purchase consideration to the respective fair values of assets acquired and liabilities assumed in the acquisition of Anixter. As the Company obtained additional information during the measurement period (one year from the acquisition date), it recorded adjustments to its preliminary estimates of fair value, which are presented in the table below. The net impact of these adjustments was an increase to goodwill of $13.4 million in the second quarter of 2021 and $16.4 million since the Company's initial estimate.
Gain (Loss) on Disposition of Business			$ (8,927,000)	0
Anixter International
Business Acquisition [Line Items]
Common stock, shares, issued (in shares) | shares					0.2397
Common stock					$ 0.01
Preferred stock, shares issued (in shares) | shares					0.6356
Preferred stock, par value (in dollars per share) | $ / shares					$ 25,000
Preferred Stock, Dividend Rate, Percentage			10.625%
Additional countries (in countries) | countries	50		50
Business Acquisition, Revenue Reported by Acquired Entity for Last Annual Period			$ 8,000,000,000
Operating Income (Loss)	$ 166,200,000	18,400,000	271,600,000	18,400,000
Business Acquisition, Adjustments to Pro Forma Net Income (Loss)		61,500,000		11,300,000
Revenues	2,500,000,000	221,900,000	4,600,000,000	221,900,000
Business Combination, Acquisition Related Costs	$ 37,700,000	$ 73,300,000	$ 84,000,000.0	$ 78,000,000.0
Business Combination, Reason for Business Combination			The Merger brought together two companies with highly compatible capabilities and characteristics. The combination of WESCO and Anixter created an enterprise with scale and should afford the Company the opportunity to digitize its business, and expand its services portfolio and supply chain offerings.
Business Acquisition, Description of Acquired Entity			Anixter was a leading distributor of network and security solutions, electrical and electronic solutions, and utility power solutions with locations in over 300 cities across approximately 50 countries, and 2019 annual sales of more than $8 billion.
Anixter International | Cash [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price | $ / shares					$ 72.82