Other (Expense) Income, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 0.1	$ 0.0	$ 0.2	$ 0.0
Net periodic postretirement benefit cost relating to Salaried VEBA	(1.4)	(1.2)	(4.5)	(3.4)
Gain on removal of Union VEBA net assets	0.0	(0.5)	0.0	0.8
Realized gain on investments	1.6	0.8	4.7	2.2
All other income (expense), net	0.4	0.7	(0.1)	0.9
Other income (expense), net	$ 0.7	$ (0.2)	$ 0.3	$ 0.5