Other (Expense) Income, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 0.0	$ 0.0	$ 0.1	$ 0.0
Net periodic postretirement benefit cost relating to Salaried VEBA	(1.6)	(1.1)	(3.1)	(2.2)
Gain on removal of Union VEBA net assets	0.0	0.0	0.0	1.3
Realized gain on investments	1.5	0.7	3.1	1.4
All other (expense) income, net	(0.4)	0.3	(0.5)	0.2
Other (expense) income, net	$ (0.5)	$ (0.1)	$ (0.4)	$ 0.7