Income Taxes - Income tax benefit (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current tax (expense) benefit
State		$ (1.6)	$ (1.9)	$ 3.1
Total current tax		(1.6)	(1.9)	3.1
Deferred tax (expense) benefit
Federal		22.2	34.2	25.5
State		(6.8)	(1.7)	5.3
Total deferred tax		15.4	32.5	30.8
Income tax (expense) benefit, net		13.8	30.6	33.9
Total income tax expense		$ 292.9	$ 7.8	$ 1.5
Refund received of remaining amount of refundable Alternative Minimum Tax carryforwards	$ 4.4