Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2016
Homebuilding revenues:
Total revenues	$ 3,251.3	$ 2,767.9	$ 6,155.5	$ 5,184.3
Income Before Income Taxes
Income before income taxes	353.9	300.5	672.1	541.8
Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	3,164.4	2,701.0	5,990.5	5,062.1
Inventory Write-down	9.4	3.2	9.4	3.7
Income Before Income Taxes
Income before income taxes	322.4	281.9	616.3	510.9
Homebuilding Inventories
Total homebuilding inventories	9,038.1		9,038.1		$ 8,340.9
Financial Services and Other [Member]
Homebuilding revenues:
Financial services revenues	86.9	66.9	165.0	122.2
Income Before Income Taxes
Income before income taxes	31.5	18.6	55.8	30.9
Financial Services Excluding Other [Member]
Income Before Income Taxes
Income before income taxes	32.2	20.1	58.8	33.3
Homebuilding and Financial Services Excluding Other [Member]
Income Before Income Taxes
Income before income taxes	354.6	302.0	675.1	544.2
Other Segments [Member]
Income Before Income Taxes
Income before income taxes	(0.7)	(1.5)	(3.0)	(2.4)
East [Member] | Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	372.6	309.0	678.6	607.2
Inventory Write-down	5.8	3.2	5.8	3.2
Income Before Income Taxes
Income before income taxes	25.9	22.6	52.2	50.4
Homebuilding Inventories
Total homebuilding inventories	1,032.1		1,032.1		891.1
Midwest [Member] | Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	168.7	162.1	319.8	285.4
Inventory Write-down	0.0	0.0	0.0	0.0
Income Before Income Taxes
Income before income taxes	0.7	8.9	10.9	15.9
Homebuilding Inventories
Total homebuilding inventories	464.3		464.3		441.2
Southeast [Member] | Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	969.0	812.0	1,852.4	1,523.6
Inventory Write-down	0.0	0.0	0.0	0.2
Income Before Income Taxes
Income before income taxes	113.1	94.5	212.7	171.4
Homebuilding Inventories
Total homebuilding inventories	2,293.1		2,293.1		2,070.3
South Central [Member] | Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	815.4	694.7	1,572.3	1,307.2
Inventory Write-down	1.4	0.0	1.4	0.0
Income Before Income Taxes
Income before income taxes	105.8	88.7	202.3	153.3
Homebuilding Inventories
Total homebuilding inventories	2,193.7		2,193.7		2,075.6
Southwest [Member] | Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	126.7	79.9	235.2	153.8
Inventory Write-down	0.0	0.0	0.0	0.0
Income Before Income Taxes
Income before income taxes	7.2	2.0	11.2	4.7
Homebuilding Inventories
Total homebuilding inventories	399.3		399.3		371.1
West [Member] | Homebuilding [Member]
Homebuilding revenues:
Homebuilding revenues	712.0	643.3	1,332.2	1,184.9
Inventory Write-down	2.2	0.0	2.2	0.3
Income Before Income Taxes
Income before income taxes	69.7	$ 65.2	127.0	$ 115.2
Homebuilding Inventories
Total homebuilding inventories	2,415.2		2,415.2		2,247.6
Corporate, Non-Segment [Member] | Homebuilding [Member]
Homebuilding Inventories
Total homebuilding inventories	$ 240.4		$ 240.4		$ 244.0