Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net sales		$ 7,523.9	$ 7,202.5	$ 6,631.2
Cost of merchandise sold		(6,094.9)	(5,821.6)	(5,369.9)
Gross Margin		1,429.0	1,380.9	1,261.3
Selling, general and administrative expenses		(1,159.9)	(1,125.0)	(1,026.6)
Depreciation and amortization		(50.5)	(49.6)	(48.9)
Other income, net		5.0	3.4	6.5
Income from Operations		223.6	209.7	192.3
Non-operating expenses		(23.7)	(30.6)	(24.8)
Income before Provision for Income Taxes		199.9	179.1	167.5
Provision for income taxes		(55.0)	(35.4)	(95.6)
Net Income		144.9	143.7	71.9
Net income attributable to noncontrolling interests		(0.4)	(0.4)	(0.3)
Net Income attributable to Graybar Electric Company, Inc.		$ 144.5	$ 143.3	$ 71.6
Net Income attributable to Graybar Electric Company, Inc. per share of Common Stock (usd per share)	[1]	$ 6.41	$ 6.37	$ 3.20
Average common shares outstanding			21.4	21.3

[1] Adjusted for the declaration of a 5% stock dividend in December 2019, shares related to which were issued in February 2020. Prior to the adjustment, the average common shares outstanding were 21.4 million shares and 21.3 million shares for the years ended December 31, 2018 and 2017, respectively.