Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax expense	$ 149.5	$ 153.1	$ 377.6	$ 350.5
Effective tax rate (percent)	19.10%	24.40%	19.60%	23.90%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount	$ 38.1		$ 77.6
Deferred tax assets net of DTL	172.2		172.2		$ 181.8
Valuation allowance for deferred income taxes	$ 13.6		$ 13.6		$ 18.7