Other (Expense) Income, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Other Income And Expenses [Abstract]
Interest income		$ 0.2	$ 0.1	$ 0.3
Net periodic postretirement benefit cost	$ (1.2)	(1.2)	(1.8)	(2.4)
Realized gain on available for sale securities		0.6		2.1
Unrealized gain on equity securities	0.1	0.7		0.1
(Loss) gain on extinguishment of debt	(35.9)		(35.9)
All other, net	0.4	0.2	0.6	(0.4)
Other (expense) income, net	$ (36.6)	$ 0.5	$ (37.0)	$ (0.3)