Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income tax expense	$ 291.8	$ 298.9
Effective tax rate (percent)	23.40%	23.60%
Deferred tax assets net of DTL	$ 190.7		$ 202.0
Valuation allowance for deferred income taxes	$ 14.8		$ 14.8