Fair Value Measurements Fair Value Measurement (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Sep. 30, 2013		Mar. 31, 2013	Sep. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 951.4		$ 936.5		$ 1,150.5	$ 1,047.7
Notes Payable	3,862.1		3,509.0
Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	930.8		913.3
Restricted Cash and Cash Equivalents	79.8		77.8
Notes Payable	3,638.3		3,270.4
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	930.8	[1]	913.3	[1]
Restricted Cash, Fair Value Disclosure	79.8	[1]	77.8	[1]
Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	930.8	[1]	913.3	[1]
Restricted Cash, Fair Value Disclosure	79.8	[1]	77.8	[1]
Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	20.6		23.2
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	20.6	[1]	23.2	[1]
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	223.8	[1]	238.6	[1]
Financial Services [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	223.8	[1]	238.6	[1]
Cash and Cash Equivalents, Fair Value Disclosure	20.6	[1]	23.2	[1]
Senior Notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	3,137.8		2,783.3
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	3,231.5	[2]	2,811.5	[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	3,231.5	[2]	2,811.5	[2]
2% convertible senior notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	495.6		478.7
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	833.5	[2]	762.4	[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	$ 833.5	[2]	$ 762.4	[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.