Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net sales	$ 7,202.5	$ 6,631.2	$ 6,385.0
Cost of merchandise sold	(5,821.6)	(5,369.9)	(5,176.6)
Gross Margin	1,380.9	1,261.3	1,208.4
Selling, general and administrative expenses	(1,125.0)	(1,026.6)	(986.3)
Depreciation and amortization	(49.6)	(48.9)	(47.9)
Other income, net	3.4	6.5	5.3
Income from Operations	209.7	192.3	179.5
Non-operating expenses	30.6	24.8	26.0
Income before Provision for Income Taxes	179.1	167.5	153.5
Provision for income taxes	(35.4)	(95.6)	(60.2)
Net Income	143.7	71.9	93.3
Net income attributable to noncontrolling interests	(0.4)	(0.3)	(0.2)
Net Income attributable to Graybar Electric Company, Inc.	$ 143.3	$ 71.6	$ 93.1
Net Income attributable to Graybar Electric Company, Inc. per share of Common Stock (usd per share)	$ 6.69	$ 3.36	$ 4.43