Business Combinations, Goodwill and Intangible Assets - Schedule of Purchase Consideration (Details) - Alcoa Warrick LLC [Member] - USD ($) $ in Millions		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2021
Business Acquisition [Line Items]
Contract purchase price	$ 670.0	$ 670.0
Working capital adjustment		31.0
Initial outstanding indebtedness – Other postretirement benefits liabilities		(83.5)
Cash paid at acquisition close on March 31, 2021		617.5
Estimated post-close adjustments		(12.7)
Preliminary purchase consideration to allocate		604.8
Revision to estimated post-close adjustments		4.4
Final purchase consideration to allocate		$ 609.2