Acquisitions (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2022	Jun. 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		$ 2,109.4		$ 2,107.6
Pro forma:
Net sales	$ 3,662.3		$ 6,679.6
Net income attributable to Reliance	$ 371.7		$ 655.7
Diluted earnings per common share attributable to Reliance shareholders (in dollars per share)	$ 5.74		$ 10.13
Basic earnings per common share attributable to Reliance shareholders (in dollars per share)	$ 5.84		$ 10.30
2021 Acquisitions
Acquisitions
Net sales		473.7
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		176.5
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		654.0
Deferred taxes		49.3
Operating lease liabilities		24.6
Other current and long-term liabilities		139.8
Total liabilities assumed		213.7
Net assets acquired		$ 440.3