Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net income attributable to Reliance	$ 302.9	$ 383.1
Denominator:
Weighted average shares outstanding (in shares)	57,340,000	58,832,000
Dilutive effect of stock-based awards (in shares)	542,000	702,000
Weighted average diluted shares outstanding (in shares)	57,882,000	59,534,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 5.28	$ 6.51
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 5.23	$ 6.43
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect	103,700	194,304