Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net income attributable to Reliance	$ 393.5	$ 395.7	$ 1,489.6	$ 991.7
Denominator:
Weighted average shares outstanding (in shares)	60,055,000	63,275,000	61,175,000	63,526,000
Dilutive effect of stock-based awards (in shares)	929,000	1,075,000	939,000	1,091,000
Weighted average diluted shares outstanding (in shares)	60,984,000	64,350,000	62,114,000	64,617,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 6.55	$ 6.25	$ 24.35	$ 15.61
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 6.45	$ 6.15	$ 23.98	$ 15.35
Diluted shares
Weighted average shares, respectively, for RSU's, not included in the diluted calculation due to their anti-dilutive effect			111,251	154,882