Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Numerator:
Net income attributable to Reliance	$ 385.1	$ 572.8	$ 768.2	$ 1,096.1
Denominator:
Weighted average shares outstanding (in shares)	58,688,000	61,657,000	58,760,000	61,744,000
Dilutive effect of stock-based awards (in shares)	658,000	937,000	680,000	944,000
Weighted average diluted shares outstanding (in shares)	59,346,000	62,594,000	59,440,000	62,688,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 6.56	$ 9.29	$ 13.07	$ 17.75
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 6.49	$ 9.15	$ 12.92	$ 17.49
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect			100,326	162,116