Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net income attributable to Reliance	$ 875.2	$ 1,335.9	$ 1,840.1
Denominator:
Weighted average shares outstanding (in shares)	55,746,000	58,328,000	60,559,000
Dilutive effect of stock-based awards (in shares)	500,000	687,000	936,000
Weighted average diluted shares outstanding (in shares)	56,246,000	59,015,000	61,495,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 15.7	$ 22.9	$ 30.39
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 15.56	$ 22.64	$ 29.92
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect	30,183	51,409	83,857