Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Income tax expense	$ (325.0)	$ (432.2)	$ (831.0)	$ (1,068.8)
Effective tax rate (percent)	23.90%	24.00%	23.50%	23.40%
Deferred tax assets net of DTL	$ 81.3		$ 81.3		$ 182.4
Valuation allowance for deferred income taxes	$ 14.8		14.8		14.9
Tax Benefit, Energy Efficient Home Credit			$ 30.8		$ 70.4