Income Taxes - Income Tax (Benefit) Expense (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current income tax (expense):
U.S. federal									$ (10.4)	$ 0.9	$ (0.1)
State									(4.2)	(3.7)	(1.4)
Non-U.S.									(1.1)	(1.7)	(2.9)
Total current income tax (expense)									(15.7)	(4.5)	(4.4)
Deferred income tax benefit (expense):
U.S. federal									23.2	(14.9)	8.3
State									10.3	(10.4)	0.0
Non-U.S.									2.7	0.5	0.1
Total deferred income tax benefit (expense)									36.2	(24.8)	8.4
Total income tax benefit (expense)	$ 117.6	$ (98.5)	$ (24.1)	$ 25.5	$ (10.4)	$ (8.8)	$ 0.1	$ (10.2)	$ 20.5	$ (29.3)	$ 4.0
U.S. statutory rate (as a percent)									21.00%	21.00%	21.00%