Income Taxes - Income tax (expense) benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current tax (expense) benefit
Federal		$ 8.8	$ (5.7)
State	$ 2.8	(1.0)	(11.9)
Total Current	2.8	7.8	(17.6)
Deferred tax (expense) benefit
Federal	(8.1)	44.8	179.6
State	3.8	12.5	(3.7)
Total Deferred	(4.3)	57.3	175.9
Income tax (expense) benefit, net	$ (1.5)	$ 65.1	$ 158.3