Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income tax expense	$ 239.1	$ 90.8
Effective tax rate (percent)	23.10%	17.40%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent		5.60%
Deferred tax assets net of DTL	$ 149.5		$ 152.4
Valuation allowance for deferred income taxes	$ 7.5		$ 7.5