Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator:
Net income attributable to Reliance	$ 572.8	$ 329.1	$ 1,096.1	$ 596.0
Denominator:
Weighted average shares outstanding (in shares)	61,657,000	63,663,000	61,744,000	63,654,000
Dilutive effect of stock-based awards (in shares)	937,000	1,130,000	944,000	1,098,000
Weighted average diluted shares outstanding (in shares)	62,594,000	64,793,000	62,688,000	64,752,000
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 9.15	$ 5.08	$ 17.49	$ 9.20
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 9.29	$ 5.17	$ 17.75	$ 9.36
Diluted shares
Weighted average shares, respectively, for RSU's, not included in the diluted calculation due to their anti-dilutive effect			162,116	230,186