Other Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Income And Expenses [Abstract]
Interest income	$ 0.2	$ 0.2	$ 0.5	$ 0.5
Net periodic postretirement benefit cost relating to Salaried VEBA	(1.1)	(1.6)	(3.5)	(4.9)
Realized gain on available for sale securities		0.9	2.1	3.0
Unrealized gain on equity securities	0.3	0.1	0.4	0.6
All other income (expense), net	0.1	(0.4)	(0.3)	0.4
Other expense, net	$ (0.5)	$ (0.8)	$ (0.8)	$ (0.4)