Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Numerator:
Net income attributable to Reliance	$ 267.8	$ 385.1	$ 570.7	$ 768.2
Denominator:
Weighted average shares outstanding (in shares)	56,878,000	58,688,000	57,109,000	58,760,000
Dilutive effect of stock-based awards (in shares)	516,000	658,000	529,000	680,000
Weighted average diluted shares outstanding (in shares)	57,394,000	59,346,000	57,638,000	59,440,000
Earnings per share attributable to Reliance stockholders - basic (in dollars per share)	$ 4.71	$ 6.56	$ 9.99	$ 13.07
Earnings per share attributable to Reliance stockholders - diluted (in dollars per share)	$ 4.67	$ 6.49	$ 9.90	$ 12.92
Diluted shares
Weighted average shares, respectively, for RSUs and PSUs, not included in the diluted calculation due to their anti-dilutive effect			56,217	100,326