Segment Information (Details) $ in Millions		3 Months Ended								12 Months Ended
		Sep. 30, 2015 USD ($) OperatingDivisions	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2015 USD ($)		Sep. 30, 2014 USD ($)		Sep. 30, 2013 USD ($)
Revenues
Revenues, Total		$ 3,172.5	$ 2,950.8	$ 2,398.0	$ 2,302.6	$ 2,472.3	$ 2,147.0	$ 1,735.0	$ 1,670.6	$ 10,824.0		$ 8,024.9		$ 6,259.3
Income (Loss) before income taxes
Income before income taxes		$ 338.8	$ 333.8	$ 230.1	$ 220.7	250.8	$ 171.8	$ 201.9	$ 189.7	1,123.4	[1]	814.2	[1]	657.8	[1]
Homebuilding [Member]
Segment Reporting Information [Line Items]
Number of Operating Segments | OperatingDivisions		39
Revenues
Homebuilding revenues										10,559.0		7,858.5		6,085.9
Inventory Impairments
Inventory impairments		$ 21.2								44.9		75.2		21.3
Income (Loss) before income taxes
Income before income taxes	[1]									1,018.3		768.8		592.3
Homebuilding inventories
Total inventories	[2]	7,807.0				7,700.5				7,807.0		7,700.5
Financial Services [Member]
Revenues
Financial Services Revenue										265.0		166.4		173.4
Income (Loss) before income taxes
Income before income taxes	[1]									105.1		45.4		65.5
East [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues										1,333.6		954.7		686.3
Inventory Impairments
Inventory impairments		6.0								14.3		17.7		0.1
Income (Loss) before income taxes
Income before income taxes	[1]									94.2		45.2		48.3
Homebuilding inventories
Total inventories	[2]	817.3				842.7				817.3		842.7
Midwest [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues										666.1		483.5		471.5
Inventory Impairments
Inventory impairments										0.0		49.3		0.0
Income (Loss) before income taxes
Income before income taxes	[1]									49.8		(9.5)		38.9
Homebuilding inventories
Total inventories	[2]	474.5				477.6				474.5		477.6
Southeast [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues										2,890.6		2,167.0		1,520.7
Inventory Impairments
Inventory impairments										8.8		3.1		0.0
Income (Loss) before income taxes
Income before income taxes	[1]									278.7		218.0		148.4
Homebuilding inventories
Total inventories	[2]	1,876.7				1,943.0				1,876.7		1,943.0
South Central [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues										2,725.2		1,971.2		1,526.2
Inventory Impairments
Inventory impairments										1.4		0.0		1.0
Income (Loss) before income taxes
Income before income taxes	[1]									296.6		208.0		149.0
Homebuilding inventories
Total inventories	[2]	1,909.0				1,742.5				1,909.0		1,742.5
Southwest [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues										336.1		285.2		327.7
Inventory Impairments
Inventory impairments										0.0		0.0		0.0
Income (Loss) before income taxes
Income before income taxes	[1]									13.1		25.5		26.3
Homebuilding inventories
Total inventories	[2]	312.4				292.9				312.4		292.9
West [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues										2,607.4		1,996.9		1,553.5
Inventory Impairments
Inventory impairments		9.0								20.4		5.1		20.2
Income (Loss) before income taxes
Income before income taxes	[1]									285.9		281.6		$ 181.4
Homebuilding inventories
Total inventories	[2]	2,165.3				2,169.4				2,165.3		2,169.4
Corporate and unallocated [Member] | Homebuilding [Member]
Homebuilding inventories
Total inventories	[2],[3]	$ 251.8				$ 232.4				$ 251.8		$ 232.4

[1] Expenses maintained at the corporate level consist primarily of interest and property taxes, which are capitalized and amortized to cost of sales or expensed directly, and the expenses related to operating the Company’s corporate office. The amortization of capitalized interest and property taxes is allocated to each segment based on the segment’s cost of sales, while those expenses associated with the corporate office are allocated to each segment based on the segment’s inventory balances.

[2] Homebuilding inventories are the only assets included in the measure of homebuilding segment assets used by the Company’s chief operating decision makers.

[3] Corporate and unallocated consists primarily of capitalized interest and property taxes.