Income Taxes - Composition of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal									$ (5.5)	$ 45.1	$ 0.0
Foreign									13.4	45.5	91.6
State									2.3	(2.3)	(0.1)
Total current tax expense									10.2	88.3	91.5
Deferred:
Federal									14.5	(56.8)	42.6
Foreign									(7.5)	(5.6)	(16.6)
State									(6.9)	1.7	(6.3)
2017 Tax Act									0.0	0.0	(33.1)
Total deferred tax expense (benefit)									0.1	(60.7)	(13.4)
Income taxes	$ 5.2	$ (22.5)	$ 14.3	$ 13.3	$ (18.6)	$ 18.6	$ 22.8	$ 4.8	$ 10.3	$ 27.6	$ 78.1