Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
U.S. Federal	$ 28.9	$ 0.0	$ 1.9
State and local	0.1	0.1	0.0
Foreign	11.7	6.8	9.9
Total current tax expense	40.7	6.9	11.8
Deferred:
U.S. Federal	(26.8)	0.8	(3.5)
State and local	0.0	0.2	(0.1)
Foreign	(1.0)	0.4	(5.0)
Total deferred tax (benefit) expense	(27.8)	1.4	(8.6)
Total income tax expense	$ 12.9	$ 8.3	$ 3.2