Other Income (Expense), Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Other Income and Expenses [Abstract]
Interest income	$ 0.4	$ 0.1	$ 0.6	$ 0.2
Net periodic postretirement benefit cost	(1.4)	(1.2)	(4.3)	(3.0)
Unrealized (loss) gain on equity securities	(0.3)		(1.4)
Loss on extinguishment of debt				(35.9)
Gain (loss) on disposition of property, plant and equipment	8.4		6.3	(0.1)
Post-acquisition funding received from Alcoa Corporation	6.0		6.0
All other, net	(0.4)	(0.1)	0.2	0.6
Other income (expense), net	$ 12.7	$ (1.2)	$ 7.4	$ (38.2)