UNAUDITED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Net sales	$ 3,420.3	$ 3,623.0	$ 10,708.4	$ 11,468.6
Costs and expenses:
Cost of sales (exclusive of depreciation and amortization shown below)	2,414.0	2,546.0	7,487.9	7,942.9
Warehouse, delivery, selling, general and administrative	665.0	626.9	2,004.2	1,928.8
Depreciation and amortization	67.9	60.6	198.1	182.5
Total costs and expenses	3,146.9	3,233.5	9,690.2	10,054.2
Operating income	273.4	389.5	1,018.2	1,414.4
Other (income) expense:
Interest expense	10.9	9.7	30.3	30.3
Other expense (income), net	2.0	(8.2)	(18.5)	(23.3)
Income before income taxes	260.5	388.0	1,006.4	1,407.4
Income tax provision	60.6	92.0	234.4	340.7
Net income	199.9	296.0	772.0	1,066.7
Less: net income attributable to noncontrolling interests	0.7	1.0	2.1	3.5
Net income attributable to Reliance	$ 199.2	$ 295.0	$ 769.9	$ 1,063.2
Earnings per share attributable to Reliance stockholders:
Basic (in dollars per share)	$ 3.64	$ 5.05	$ 13.68	$ 18.13
Diluted (in dollars per share)	$ 3.61	$ 4.99	$ 13.55	$ 17.92
Shares used in computing earnings per share:
Basic (in shares)	54,691	58,427	56,297	58,648
Diluted (in shares)	55,182	59,124	56,813	59,333