Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Numerator:
Net income attributable to Reliance	$ 383.1	$ 523.3
Denominator:
Weighted average shares outstanding (in shares)	58,832,000	61,833,000
Dilutive effect of stock-based awards (in shares)	702,000	951,000
Weighted average diluted shares outstanding (in shares)	59,534,000	62,784,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 6.51	$ 8.46
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 6.43	$ 8.33
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect	194,304	314,042