Commitments and Contingencies - Warranty Liability (Details) - Homebuilding [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Changes in warranty liability
Warranty liability, beginning of year	$ 82.0	$ 65.7
Warranties issued	54.2	47.2
Changes in liability for pre-existing warranties	13.9	5.6
Settlements made	(45.7)	(36.5)
Warranty liability, end of year	$ 104.4	$ 82.0