Fair Value Measurements - Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Homebuilding [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Debt securities collateralized by residential real estate	$ 0.0	$ 33.9
Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Mortgage loans held for sale	654.0	631.0
Recurring [Member] | Level 1 [Member] | Homebuilding [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Debt securities collateralized by residential real estate		0.0
Recurring [Member] | Level 1 [Member] | Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Mortgage loans held for sale	0.0	0.0
Recurring [Member] | Level 1 [Member] | Financial Services [Member] | Interest rate lock commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	0.0	0.0
Recurring [Member] | Level 1 [Member] | Financial Services [Member] | Forward Sales Of MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	0.0	0.0
Recurring [Member] | Level 1 [Member] | Financial Services [Member] | Best-efforts and mandatory commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	0.0	0.0
Recurring [Member] | Level 2 [Member] | Homebuilding [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Debt securities collateralized by residential real estate		0.0
Recurring [Member] | Level 2 [Member] | Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Mortgage loans held for sale	640.9	617.1
Recurring [Member] | Level 2 [Member] | Financial Services [Member] | Interest rate lock commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	9.3	3.6
Recurring [Member] | Level 2 [Member] | Financial Services [Member] | Forward Sales Of MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	(2.6)	(6.0)
Recurring [Member] | Level 2 [Member] | Financial Services [Member] | Best-efforts and mandatory commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	(0.2)	(1.1)
Recurring [Member] | Level 3 [Member] | Homebuilding [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Debt securities collateralized by residential real estate	0.0	33.9	$ 20.8
Recurring [Member] | Level 3 [Member] | Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Mortgage loans held for sale	6.8	13.9	$ 12.0
Recurring [Member] | Level 3 [Member] | Financial Services [Member] | Interest rate lock commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	0.0	0.0
Recurring [Member] | Level 3 [Member] | Financial Services [Member] | Forward Sales Of MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	0.0	0.0
Recurring [Member] | Level 3 [Member] | Financial Services [Member] | Best-efforts and mandatory commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	0.0	0.0
Estimate fair value [Member] | Recurring [Member] | Homebuilding [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Debt securities collateralized by residential real estate		33.9
Estimate fair value [Member] | Recurring [Member] | Financial Services [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Mortgage loans held for sale	647.7	631.0
Estimate fair value [Member] | Recurring [Member] | Financial Services [Member] | Interest rate lock commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	9.3	3.6
Estimate fair value [Member] | Recurring [Member] | Financial Services [Member] | Forward Sales Of MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	(2.6)	(6.0)
Estimate fair value [Member] | Recurring [Member] | Financial Services [Member] | Best-efforts and mandatory commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]
Derivatives not designated as hedging instruments	$ (0.2)	$ (1.1)