Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income tax expense	$ 295.7	$ 441.0	$ 594.6	$ 792.5
Effective tax rate (percent)	23.70%	23.40%	23.70%	23.40%
Deferred tax assets net of DTL	$ 130.1		$ 130.1		$ 159.0
Valuation allowance for deferred income taxes	$ 17.8		$ 17.8		$ 17.9