Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax expense	$ 90.8	$ 89.0
Effective tax rate (percent)	17.40%	23.70%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount	$ 32.9
Deferred tax assets net of DTL	172.4		$ 181.8
Valuation allowance for deferred income taxes	$ 18.3		$ 18.7