Income Taxes - Income Tax Provision (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 108.9	$ 40.0	$ 30.3
State	50.3	24.0	11.5
Current income tax expense (benefit)	159.2	64.0	41.8
Deferred:
Federal	17.6	34.7	20.4
State	1.4	5.2	9.6
Deferred income tax expense (benefit)	19.0	39.9	30.0
Total	$ 178.2	$ 103.9	$ 71.8

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