Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income attributable to Reliance	$ 1,335.9	$ 1,840.1	$ 1,413.0
Denominator:
Weighted average shares outstanding (in shares)	58,328,000	60,559,000	63,217,000
Dilutive effect of stock-based awards (in shares)	687,000	936,000	1,110,000
Weighted average diluted shares outstanding (in shares)	59,015,000	61,495,000	64,327,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 22.90	$ 30.39	$ 22.35
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 22.64	$ 29.92	$ 21.97
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect	51,409	83,857	116,206