Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Current:
Federal	$ 12.5	$ 10.1	$ (5.3)
State	5.0	5.0	2.4
Deferred:
Federal	(19.6)	0.8	(54.5)
State	(7.5)	(3.1)	(8.8)
Total income tax (benefit) expense	$ (9.6)	$ 12.8	$ (66.2)