Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other Income And Expenses [Abstract]
Interest income	$ 0.1	$ 0.2	$ 0.2	$ 0.5
Net periodic postretirement benefit cost	(1.2)	(1.1)	(3.0)	(3.5)
Realized gain on available for sale securities				2.1
Unrealized gain on equity securities		0.3		0.4
Gain (loss) on extinguishment of debt			(35.9)
All other, net	(0.1)	0.1	0.5	(0.3)
Other expense, net	$ (1.2)	$ (0.5)	$ (38.2)	$ (0.8)