Stockholder's Equity - Schedule of Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized foreign currency translation losses, net of income tax benefit of $0.4 and $0.4, respectively	$ (7.5)	$ (27.5)
Unrealized loss on available-for-sale securities, net of income tax benefit of $0.1 million	(0.3)	0.0
Net loss from pension and other postretirement benefit liabilities, net of income tax benefits of $28.8 million and $36.8 million, respectively (a)	(86.3)	(64.5)
Accumulated other comprehensive loss	(94.1)	(92.0)
Accumulated other comprehensive income (loss), available-for-sale securities adjustment, tax effect	0.1	0.0
Foreign currency translation losses, tax benefit	0.4	0.0
Net loss from pension and other postretirement benefit liabilities, tax benefit	28.9	$ 36.8
Reclassification of the stranded tax effects related to the Tax Act (Note 10)	(10.9)
Retained Earnings
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification of the stranded tax effects related to the Tax Act (Note 10)	$ 10.9