Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Revenues
Revenues, Total	$ 3,741.3	$ 3,231.9	$ 2,767.9	$ 2,416.4	$ 3,172.5	$ 2,950.8	$ 2,398.0	$ 2,302.6	$ 12,157.4	$ 10,824.0	$ 8,024.9
Income (Loss) before income taxes
Income before income taxes	433.0	$ 378.6	$ 300.5	$ 241.3	338.8	$ 333.8	$ 230.1	$ 220.7	1,353.5	1,123.4	814.2
Homebuilding [Member]
Revenues
Homebuilding revenues									11,861.8	10,559.0	7,858.5
Inventory Impairments
Inventory impairments	11.4								20.3	44.9	75.2
Income (Loss) before income taxes
Income before income taxes									1,264.4	1,018.3	768.5
Homebuilding inventories
Total inventories	8,340.9				7,807.0				8,340.9	7,807.0
Financial Services Excluding Other [Member]
Income (Loss) before income taxes
Income before income taxes									98.1	105.1	45.4
Homebuilding and Financial Services [Member]
Income (Loss) before income taxes
Income before income taxes									1,362.5	1,123.4	813.9
Financial Services [Member]
Revenues
Financial Services Revenue									295.6	265.0	166.4
Income (Loss) before income taxes
Income before income taxes									89.1	105.1	45.7
Other Segments [Member]
Income (Loss) before income taxes
Income before income taxes									(9.0)	0.0	0.3
East [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues									1,446.5	1,333.6	954.7
Inventory Impairments
Inventory impairments									12.3	14.3	17.7
Income (Loss) before income taxes
Income before income taxes									138.7	94.2	45.2
Homebuilding inventories
Total inventories	891.1				817.3				891.1	817.3
Midwest [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues									651.7	666.1	483.5
Inventory Impairments
Inventory impairments									0.0	0.0	49.3
Income (Loss) before income taxes
Income before income taxes									44.3	49.8	(9.6)
Homebuilding inventories
Total inventories	441.2				474.5				441.2	474.5
Southeast [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues									3,463.5	2,890.6	2,167.0
Inventory Impairments
Inventory impairments									0.7	8.8	3.1
Income (Loss) before income taxes
Income before income taxes									388.4	278.7	217.9
Homebuilding inventories
Total inventories	2,070.3				1,876.7				2,070.3	1,876.7
South Central [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues									2,995.1	2,725.2	1,971.2
Inventory Impairments
Inventory impairments									1.0	1.4	0.0
Income (Loss) before income taxes
Income before income taxes									374.8	296.6	207.9
Homebuilding inventories
Total inventories	2,075.6				1,909.0				2,075.6	1,909.0
Southwest [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues									388.1	336.1	285.2
Inventory Impairments
Inventory impairments									6.0	0.0	0.0
Income (Loss) before income taxes
Income before income taxes									7.3	13.1	25.5
Homebuilding inventories
Total inventories	371.1				312.4				371.1	312.4
West [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues									2,916.9	2,607.4	1,996.9
Inventory Impairments
Inventory impairments									0.3	20.4	5.1
Income (Loss) before income taxes
Income before income taxes									310.9	285.9	$ 281.6
Homebuilding inventories
Total inventories	2,247.6				2,165.3				2,247.6	2,165.3
Corporate and unallocated [Member] | Homebuilding [Member]
Homebuilding inventories
Total inventories	$ 244.0				$ 251.8				$ 244.0	$ 251.8