Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Income and Expenses [Abstract]
Interest income	$ 0.1	$ 0.0
Net periodic postretirement benefit cost relating to Salaried VEBA	(1.5)	(1.1)
Gain on removal of Union VEBA net assets	0.0	1.3
Realized gain on investments	1.6	0.7
All other expense, net	(0.1)	(0.1)
Other income, net	$ 0.1	$ 0.8