Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	$ 661.8		$ 977.4		$ 1,086.8	$ 770.5
Notes payable, carrying value	3,682.8		3,509.0
Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	632.5	[1]	954.2	[1]
Restricted cash, carrying value	10.0	[1]	77.8	[1]
Notes payable, carrying value	3,323.6		3,270.4
Homebuilding [Member] | Senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, carrying value	3,000.2	[2]	2,783.3	[2]
Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying value	29.3	[1]	23.2	[1]
Assets Sold under Agreements to Repurchase, Repurchase Liability	359.2	[1]	238.6	[1]
Level 1 [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	632.5	[1]	954.2	[1]
Restricted cash, fair value	10.0	[1]	77.8	[1]
Level 1 [Member] | Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	29.3	[1]	23.2	[1]
Level 2 [Member] | Homebuilding [Member] | Senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value	3,033.8	[2]	2,811.5	[2]
Level 2 [Member] | Homebuilding [Member] | Convertible Senior Note One [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value			762.4	[2]
Level 3 [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Line of Credit Facility, Fair Value of Amount Outstanding	300.0	[1]
Level 3 [Member] | Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage repurchase facility, fair value	359.2	[1]	238.6	[1]
Estimate fair value [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	632.5	[1]	954.2	[1]
Restricted cash, fair value	10.0	[1]	77.8	[1]
Line of Credit Facility, Fair Value of Amount Outstanding	300.0	[1]
Estimate fair value [Member] | Homebuilding [Member] | Senior notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value	3,033.8	[2]	2,811.5	[2]
Estimate fair value [Member] | Homebuilding [Member] | Convertible Senior Note One [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, fair value			762.4	[2]
Estimate fair value [Member] | Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	29.3	[1]	23.2	[1]
Mortgage repurchase facility, fair value	359.2	[1]	238.6	[1]
Convertible Senior Note One [Member] | Homebuilding [Member] | Unsecured Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable, carrying value	$ 0	[2]	$ 478.7	[2]

[1] The fair value approximates carrying value due to its short-term nature, short maturity or floating interest rate terms, as applicable.

[2] The fair value is determined based on quoted market prices of recent transactions of the notes, which is classified as Level 2 within the fair value hierarchy.