Income Taxes - Components of Income Tax Benefit (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax benefit (expense)
Federal	$ (12.5)	$ (15.3)	$ (16.3)
State	(9.2)	(6.4)	(6.1)
Foreign	(0.2)	(1.4)	3.0
Total current	(21.9)	(23.1)	(19.4)
Deferred tax benefit (expense)
Federal	(16.7)	14.6	480.7
State	(4.4)	10.9	39.3
Foreign	0.0	1.2	(2.1)
Total deferred	(21.1)	26.7	517.9
Total income tax benefit (expense)	$ (43.0)	$ 3.6	$ 498.5