Acquisitions (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Allocation of the total purchase price of the acquisitions to the fair value of the assets acquired and liabilities assumed
Goodwill		$ 2,103.9		$ 2,107.6
Pro forma:
Net sales	$ 4,100.8		$ 10,780.4
Net income attributable to Reliance	$ 435.5		$ 1,091.2
Basic earnings per common share attributable to Reliance shareholders (in dollars per share)	$ 6.88		$ 17.18
Diluted earnings per common share attributable to Reliance shareholders (in dollars per share)	$ 6.77		$ 16.89
2021 Acquisitions
Acquisitions
Net sales		681.7
Allocation of the total purchase price of the acquisitions to the fair value of the assets acquired and liabilities assumed
Cash		1.0
Accounts receivable		107.2
Inventories		134.4
Property, plant and equipment		33.6
Operating lease right-of-use assets		29.8
Goodwill		177.0
Intangible assets subject to amortization		116.3
Intangible assets not subject to amortization		51.2
Other current and long-term assets		4.0
Total assets acquired		654.5
Deferred taxes		49.3
Operating lease liabilities		24.6
Other current and long-term liabilities		140.3
Total liabilities assumed		214.2
Net assets acquired		$ 440.3