Notes Payable - Principal Amounts (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Summary of notes payable at principal amounts, net of unamortized discounts
Notes payable	$ 2,871.6	$ 3,271.3
Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Notes payable	2,451.6	2,798.3
Financial Services [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Mortgage repurchase facility	420.0	473.0
Line of Credit [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Line of credit, amount outstanding	$ 0.0	0.0
Unsecured Debt [Member] \| Senior Note Twenty Four [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	4.75%
Notes payable	$ 0.0	349.5
Unsecured Debt [Member] \| Senior Note Twenty Six [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	3.625%
Notes payable	$ 399.7	398.9
Unsecured Debt [Member] \| Senior Note Twenty Nine [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	3.75%
Notes payable	$ 498.8	498.0
Unsecured Debt [Member] \| Senior Note Member Thirty [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	4.00%
Notes payable	$ 497.9	497.1
Unsecured Debt [Member] \| Senior Note Member Twenty Five [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	4.375%
Notes payable	$ 348.1	347.7
Unsecured Debt [Member] \| Senior Note Twenty Seven [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	4.75%
Notes payable	$ 298.4	298.2
Unsecured Debt [Member] \| SeniorNoteTwentyEight [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Senior notes, stated interest rate	5.75%
Notes payable	$ 397.6	397.3
Secured Debt [Member] \| Homebuilding [Member]
Summary of notes payable at principal amounts, net of unamortized discounts
Notes payable	$ 11.1	$ 11.6

Amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Section S99
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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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