Business Combinations, Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Mar. 31, 2021
Gross carrying value:
Beginning balance	$ 37.2	$ 37.2
Ending balance	57.7	37.2
Accumulated impairment loss	(18.4)	(18.4)
Net carrying value	39.3	18.8
Alcoa Warrick LLC [Member]
Gross carrying value:
Warrick acquisition	20.5	$ 0.0
Net carrying value	$ 20.5		$ 27.4