Income Taxes - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Current
Federal	$ 8.0	$ 9.4	$ (0.9)
State	(5.5)	4.3	2.1
Non-U.S.	1.0	3.0	1.8
Current income tax expense	3.5	16.7	3.0
Deferred
Federal	36.8	16.2	47.7
State	(3.2)	1.3	9.0
Non-U.S.	0.0	0.5	0.2
Deferred income tax expense	33.6	18.0	56.9
Income tax expense	$ 37.1	$ 34.7	$ 59.9