Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Revenues
Total revenues	$ 3,776.4	$ 3,231.9	$ 9,931.9	$ 8,416.2
Income Before Income Taxes
Income before income taxes	444.5	378.6	1,116.5	920.4
Homebuilding [Member]
Revenues
Homebuilding revenues	3,684.5	3,148.8	9,675.0	8,210.8
Inventory Impairments
Inventory Write-down	1.0	5.2	10.4	8.9
Income Before Income Taxes
Income before income taxes	415.2	348.4	1,031.5	859.3
Homebuilding Inventories
Total homebuilding inventories	9,554.0		9,554.0		$ 8,340.9
Financial Services and Other [Member]
Revenues
Financial services revenues	91.9	83.1	256.9	205.4
Income Before Income Taxes
Income before income taxes	29.3	30.2	85.0	61.1
Financial Services Excluding Other [Member]
Income Before Income Taxes
Income before income taxes	33.9	31.3	92.7	64.6
Homebuilding and Financial Services Excluding Other [Member]
Income Before Income Taxes
Income before income taxes	449.1	379.7	1,124.2	923.9
Other Segments [Member]
Income Before Income Taxes
Income before income taxes	(4.6)	(1.1)	(7.7)	(3.5)
East [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues	482.2	391.2	1,160.7	998.3
Inventory Impairments
Inventory Write-down	0.0	4.2	5.8	7.4
Income Before Income Taxes
Income before income taxes	54.2	40.3	106.4	90.6
Homebuilding Inventories
Total homebuilding inventories	1,077.1		1,077.1		891.1
Midwest [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues	202.2	179.9	522.0	465.2
Inventory Impairments
Inventory Write-down	1.0	0.0	1.0	0.0
Income Before Income Taxes
Income before income taxes	17.9	13.4	28.8	29.4
Homebuilding Inventories
Total homebuilding inventories	483.2		483.2		441.2
Southeast [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues	1,136.3	913.3	2,988.7	2,436.9
Inventory Impairments
Inventory Write-down	0.0	0.0	0.0	0.2
Income Before Income Taxes
Income before income taxes	128.6	107.6	341.3	279.0
Homebuilding Inventories
Total homebuilding inventories	2,370.3		2,370.3		2,070.3
South Central [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues	924.8	816.1	2,497.1	2,123.4
Inventory Impairments
Inventory Write-down	0.0	1.0	1.4	1.0
Income Before Income Taxes
Income before income taxes	119.1	109.3	321.4	262.6
Homebuilding Inventories
Total homebuilding inventories	2,227.6		2,227.6		2,075.6
Southwest [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues	152.6	93.0	387.8	246.8
Inventory Impairments
Inventory Write-down	0.0	0.0	0.0	0.0
Income Before Income Taxes
Income before income taxes	14.8	0.9	26.0	5.6
Homebuilding Inventories
Total homebuilding inventories	547.9		547.9		371.1
West [Member] | Homebuilding [Member]
Revenues
Homebuilding revenues	786.4	755.3	2,118.7	1,940.2
Inventory Impairments
Inventory Write-down	0.0	0.0	2.2	0.3
Income Before Income Taxes
Income before income taxes	80.6	$ 76.9	207.6	$ 192.1
Homebuilding Inventories
Total homebuilding inventories	2,611.2		2,611.2		2,247.6
Corporate, Non-Segment [Member] | Homebuilding [Member]
Homebuilding Inventories
Total homebuilding inventories	$ 236.7		$ 236.7		$ 244.0