Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net sales	$ 1,204.9	$ 1,057.1	$ 2,435.7	$ 1,998.4
Cost of materials sold	993.1	871.8	1,992.6	1,648.2
Gross profit	211.8	185.3	443.1	350.2
Warehousing, delivery, selling, general, and administrative	164.6	138.9	328.3	269.4
Restructuring and other charges	1.1		1.4
Operating profit	46.1	46.4	113.4	80.8
Other income and (expense), net	(0.2)	1.1	(1.0)	4.7
Interest and other expense on debt	(23.9)	(23.9)	(47.8)	(47.2)
Income before income taxes	22.0	23.6	64.6	38.3
Provision for income taxes	5.5	6.2	18.5	10.3
Net income	16.5	17.4	46.1	28.0
Less: Net income (loss) attributable to noncontrolling interest	0.1	(0.1)	0.2	0.1
Net income attributable to Ryerson Holding Corporation	16.4	17.5	45.9	27.9
Comprehensive income	17.5	15.2	50.6	24.8
Less: Comprehensive income attributable to noncontrolling interest	0.1		0.3	0.2
Comprehensive income attributable to Ryerson Holding Corporation	$ 17.4	$ 15.2	$ 50.3	$ 24.6
Basic earnings per share	$ 0.43	$ 0.47	$ 1.22	$ 0.75
Diluted earnings per share	$ 0.43	$ 0.46	$ 1.21	$ 0.74