Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income tax expense	$ 111.2	$ 83.6
Effective tax rate (percent)	35.00%	34.60%
Deferred tax assets net of DTL	$ 478.1		$ 486.6
Homebuilding [Member]
Income Tax Contingency [Line Items]
Valuation allowance for deferred income taxes	$ 10.3		$ 10.3