Other Income (Expense), Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other Income and Expenses [Abstract]
Interest income	$ 1.3	$ 0.2	$ 0.6
Net periodic postretirement benefit cost	(5.6)	(4.1)	(4.7)
Realized gain on available for sale securities			2.0
Unrealized (loss) gain on equity securities	(1.2)	(0.2)	0.7
Gain (loss) on extinguishment of debt - Note 9		(35.9)
Gain (loss) on disposition of property, plant and equipment	6.0	0.5	(0.2)
Post-acquisition funding received from Alcoa Corporation	6.0
All other, net	(0.1)	0.6	0.2
Other income (expense), net	$ 6.4	$ (38.9)	$ (1.4)