Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Numerator:
Net income attributable to Reliance	$ 523.3	$ 266.9
Denominator:
Weighted average shares outstanding (in shares)	61,833,000	63,645,000
Dilutive effect of stock-based awards (in shares)	951,000	1,066,000
Weighted average diluted shares outstanding (in shares)	62,784,000	64,711,000
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 8.33	$ 4.12
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 8.46	$ 4.19
Diluted shares
Weighted average shares, respectively, for RSU's, not included in the diluted calculation due to their anti-dilutive effect	314,042	452,124