Income Taxes - Unrecognized Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 2.9	$ 2.9	$ 8.9
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	0.0	1.5
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	0.0	0.0
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0.0	(7.5)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 2.9	$ 2.9