Income Taxes - Components of Income Tax Benefit (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current tax benefit (expense)
Federal	$ 47.0	$ (12.5)	$ (15.3)
State	0.2	(9.2)	(6.4)
Foreign	(0.4)	(0.2)	(1.4)
Total current	46.8	(21.9)	(23.1)
Deferred tax benefit (expense)
Federal	103.6	(16.7)	14.6
State	14.7	(4.4)	10.9
Foreign	0.0	0.0	1.2
Total deferred	118.3	(21.1)	26.7
Total income tax benefit (expense)	$ 165.1	$ (43.0)	$ 3.6