Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Business Information [Line Items]
Property, Plant and Equipment, Net	$ 195.4	$ 146.9
Other Assets	499.6	527.3
Cash and cash equivalents	1,303.2	1,383.8	$ 661.8	$ 977.4
Deferred profit on sales	3.6	2.0
Advertising expense	41.2	42.4	44.0
Other Segments [Member]
Business Information [Line Items]
Property, Plant and Equipment, Net		19.2
Other Assets		1.2
Cash and cash equivalents		1.1
Other Accounts Payable and Accrued Liabilities		1.8
General and Administrative Expense		10.6	7.3
Other Operating Income		10.6	$ 7.6
Homebuilding [Member]
Business Information [Line Items]
Property, Plant and Equipment, Net	139.5	124.8
Other Assets	456.2	455.0
Cash and cash equivalents	1,271.8	1,354.8
Earnest Money Deposits	167.0
Homebuilding [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Business Information [Line Items]
Earnest Money Deposits	149.5	74.4
Subsidiaries [Member]
Business Information [Line Items]
Cash and cash equivalents	$ 40.5	$ 40.5