Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018
Current:
Federal	$ 23.2	$ 10.1	$ (5.3)
State	2.4	5.0	2.4
Deferred:
Federal	(30.5)	0.8	(54.5)
State	(4.3)	(3.1)	(8.8)
Total income tax expense (benefit)	$ (9.2)	$ 12.8	$ (66.2)