Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net sales	$ 1,575.1	$ 831.5	$ 4,141.4	$ 2,613.6
Cost of materials sold	1,210.5	675.6	3,321.9	2,146.4
Gross profit	364.6	155.9	819.5	467.2
Warehousing, delivery, selling, general, and administrative	180.2	125.4	530.3	405.2
Gain on sale of assets			(107.7)
Restructuring and other charges		0.2		2.2
Operating profit	184.4	30.3	396.9	59.8
Other income and (expense), net	(0.8)	0.5	(1.2)	0.4
Pension settlement charge due to annuitization	(98.3)	(52.5)	(98.3)	(52.5)
Loss on retirement of debt	(5.5)	(17.1)	(5.5)	(16.2)
Interest and other expense on debt	(13.7)	(20.2)	(40.8)	(61.2)
Income (loss) before income taxes	66.1	(59.0)	251.1	(69.7)
Provision (benefit) for income taxes	16.1	(19.3)	62.2	(20.9)
Net income (loss)	50.0	(39.7)	188.9	(48.8)
Less: Net income attributable to noncontrolling interest	0.3	0.2	1.0	0.3
Net income (loss) attributable to Ryerson Holding Corporation	49.7	(39.9)	187.9	(49.1)
Comprehensive income (loss)	137.6	(32.4)	282.9	(48.1)
Less: Comprehensive income attributable to noncontrolling interest	0.2	0.2	0.9	0.2
Comprehensive income (loss) attributable to Ryerson Holding Corporation	$ 137.4	$ (32.6)	$ 282.0	$ (48.3)
Basic earnings (loss) per share	$ 1.29	$ (1.05)	$ 4.90	$ (1.29)
Diluted earnings (loss) per share	1.27	$ (1.05)	4.84	$ (1.29)
Dividends declared per share	$ 0.08		$ 0.08