Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income tax expense	$ 441.0	$ 246.0	$ 792.5	$ 485.1
Effective tax rate (percent)	23.40%	20.80%	23.40%	21.90%
Deferred tax assets net of DTL	$ 135.7		$ 135.7		$ 159.5
Valuation allowance for deferred income taxes	$ 4.0		$ 4.0		$ 4.2