Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net income attributable to Reliance	$ 199.2	$ 295.0	$ 769.9	$ 1,063.2
Denominator:
Weighted average shares outstanding (in shares)	54,691,000	58,427,000	56,297,000	58,648,000
Dilutive effect of stock-based awards (in shares)	491,000	697,000	516,000	685,000
Weighted average diluted shares outstanding (in shares)	55,182,000	59,124,000	56,813,000	59,333,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 3.64	$ 5.05	$ 13.68	$ 18.13
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 3.61	$ 4.99	$ 13.55	$ 17.92
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect			39,716	68,453