Fair Value Measurements Fair Value Measurement (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Sep. 30, 2012		Jun. 30, 2012	Sep. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 638.0		$ 1,047.7		$ 904.9	$ 732.6
Restricted Cash and Cash Equivalents	68.6		49.3
Notes Payable	3,083.6		2,493.1
Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	607.8		1,030.4
Restricted Cash and Cash Equivalents	68.6		49.3
Notes Payable	2,863.9		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	607.8		1,030.4
Restricted Cash, Fair Value Disclosure	68.6		49.3
Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	607.8	[1]	1,030.4	[1]
Restricted Cash, Fair Value Disclosure	68.6	[1]	49.3	[1]
Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	30.2		17.3
Mortgage repurchase facility, maturing 2014	219.7		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	30.2		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	219.7		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	30.2	[1]	17.3	[1]
Mortgage Repurchase Facility Liability, Fair Value Disclosure	219.7	[1]	187.8	[1]
Senior Notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	2,383.1	[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	2,409.8	[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	2,409.8	[2]	1,973.9	[2]
2% convertible senior notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	470.5		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	831.2	[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	$ 831.2	[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 of the notes, which is classified as Level 2 within the fair value hierarchy.