Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2016	Sep. 30, 2015
Deferred tax assets:
Inventory costs	$ 87.6	$ 113.7
Inventory impairments	128.3	180.4
Warranty and construction defect costs	138.8	127.1
Net operating loss carryforwards	40.1	58.5
Tax credit carryforwards	2.9	7.6
Incentive compensation plans	82.2	79.3
Deferral of profit on home sales	2.2	2.0
Other	11.1	14.4
Total deferred tax assets	493.2	583.0
Valuation allowance	(10.3)	(10.1)
Total deferred tax assets, net of valuation allowance	482.9	572.9
Deferred tax liabilities	6.6	14.8
Deferred income taxes, net	$ 476.3	$ 558.1