Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Income And Expenses [Abstract]
Interest income	$ 0.1	$ 0.1
Net periodic postretirement benefit cost relating to Salaried VEBA	(0.6)	(1.2)
Realized gain on available for sale securities		1.5
Unrealized loss on equity securities	(0.1)	(0.6)
All other, net	0.2	(0.6)
Other expense, net	$ (0.4)	$ (0.8)