Income Taxes - Income Tax Provision (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal	$ 40.0	$ 30.3	$ 95.1
State	24.0	11.5	16.9
Current income tax expense (benefit)	64.0	41.8	112.0
Deferred:
Federal	34.7	20.4	(14.2)
State	5.2	9.6	4.1
Deferred income tax expense (benefit)	39.9	30.0	(10.1)
Total	$ 103.9	$ 71.8	$ 101.9