Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net sales	$ 1,147.3	$ 1,010.3
Cost of materials sold	949.4	814.5
Gross profit	197.9	195.8
Warehousing, delivery, selling, general, and administrative	171.8	155.7
Gain on sale of assets	(20.3)
Operating profit	46.4	40.1
Other income and (expense), net	0.3	0.9
Interest and other expense on debt	(13.5)	(21.7)
Income before income taxes	33.2	19.3
Provision for income taxes	7.6	2.9
Net income	25.6	16.4
Less: Net income attributable to noncontrolling interest	0.3
Net income attributable to Ryerson Holding Corporation	25.3	16.4
Comprehensive income	28.0	6.2
Less: Comprehensive income attributable to noncontrolling interest	0.2
Comprehensive income attributable to Ryerson Holding Corporation	$ 27.8	$ 6.2
Basic earnings per share	$ 0.66	$ 0.43
Diluted earnings per share	$ 0.66	$ 0.43