Fair Value Measurements Fair Value Measurement (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Sep. 30, 2012		Dec. 31, 2011	Sep. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 566.9		$ 1,047.7		$ 738.1	$ 732.6
Notes Payable	2,593.7		2,493.1
Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	546.4		1,030.4
Restricted Cash and Cash Equivalents	54.8		49.3
Line of Credit Facility, Amount Outstanding	100.0		0
Notes Payable	2,424.3		2,305.3
Homebuilding [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	546.4		1,030.4
Restricted Cash and Cash Equivalents	54.8
Restricted Cash, Fair Value Disclosure			49.3
Homebuilding [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of Credit, Fair Value Disclosure	100.0
Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	546.4	[1]	1,030.4	[1]
Restricted Cash, Fair Value Disclosure	54.8	[1]	49.3	[1]
Lines of Credit, Fair Value Disclosure	100.0	[1]
Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	20.5		17.3
Mortgage repurchase facility, maturing 2013	169.4		187.8
Financial Services [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	20.5		17.3
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage Repurchase Facility Liability, Fair Value Disclosure	169.4		187.8
Financial Services [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	20.5	[1]	17.3	[1]
Mortgage Repurchase Facility Liability, Fair Value Disclosure	169.4	[1]	187.8	[1]
Senior Notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	1,854.5	[2]	1,854.2	[2]
Senior Notes [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	1,961.3	[2]	1,973.9	[2]
Senior Notes [Member] | Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	1,961.3	[2]	1,973.9	[2]
2% convertible senior notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	454.6		447.0
2% convertible senior notes [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	791.6	[2]	821.2	[2]
2% convertible senior notes [Member] | Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	$ 791.6	[2]	$ 821.2	[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, which is classified as Level 2 within the fair value hierarchy.