Income Taxes - Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income tax expense attributable to income from operations	$ 70.1	$ 37.8	$ 37.1
Taxes allocated to stockholders’ equity, related to pension liabilities	(0.1)	0.5	0.0
Taxes allocated to stockholders’ equity, related to hedge accounting	(17.0)	0.0	0.0
Total income tax expense	$ 53.0	$ 38.3	$ 37.1