Segment Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Assets
Cash and cash equivalents	$ 2,985.4	$ 4,516.4
Restricted cash	47.9	27.6
Inventories:
Construction in progress and finished homes	7,648.5	8,875.8
Residential land and lots — developed and under development	14,695.8	12,948.1
Land held for development	218.3	160.6
Land held for sale	21.4	12.7
Rental properties	2,703.3	2,906.0
Total inventories	25,287.3	24,903.2	$ 22,373.3
Mortgage loans held for sale	2,566.5	2,477.5
Deferred income taxes, net	44.5	167.5
Property and equipment, net	578.9	531.0
Other Assets	3,797.2	3,317.6
Goodwill	163.5	163.5
Total assets	35,471.2	36,104.3
Liabilities
Accounts payable	1,221.9	1,345.5
Accrued expenses and other liabilities	3,541.6	3,016.7
Notes payable	5,965.5	5,917.7
Total liabilities	10,729.0	10,279.9
Revenues:
Revenues	34,250.4	36,801.4	35,460.4
Cost of sales:
Inventory and land option charges	158.1	78.8	80.3
Cost of sales	26,134.2	27,266.0	26,110.0
Selling, general and administrative expense	3,692.0	3,599.5	3,248.8
Other (income) expense (3)	315.7	348.8	213.1
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	4,739.9	6,284.7	6,314.7
Depreciation and amortization	101.3	87.1	91.6
Cash provided by (used in) operating activities	3,420.9	2,189.8	4,304.1
Home Building
Assets
Cash and cash equivalents	2,210.5	3,623.0
Restricted cash	25.5	4.8
Inventories:
Construction in progress and finished homes	7,743.7	8,986.1
Residential land and lots — developed and under development	12,513.1	11,011.7
Land held for development	38.3	20.5
Land held for sale	21.4	12.7
Rental properties	0.0	0.0
Total inventories	20,316.5	20,031.0	18,155.8
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	125.7	211.6
Property and equipment, net	543.0	500.2
Other Assets	3,344.1	2,976.5
Goodwill	134.3	134.3
Total assets	26,699.6	27,481.4
Liabilities
Accounts payable	1,016.8	1,046.1
Accrued expenses and other liabilities	3,122.1	2,552.0
Notes payable	3,154.4	2,926.8
Total liabilities	7,293.3	6,524.9
Revenues:
Revenues	31,515.5	33,961.8	31,743.2
Cost of sales:
Inventory and land option charges	144.2	68.9	60.7
Cost of sales	24,859.2	26,061.0	24,315.8
Selling, general and administrative expense	2,623.1	2,553.3	2,239.9
Other (income) expense (3)	101.7	107.6	78.8
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	4,134.9	5,455.1	5,266.3
Depreciation and amortization	93.4	79.4	64.0
Cash provided by (used in) operating activities	3,407.6	2,239.0	3,078.4
Rental
Assets
Cash and cash equivalents	140.8	157.6
Restricted cash	2.5	2.2
Inventories:
Construction in progress and finished homes	0.0	0.0
Residential land and lots — developed and under development	0.0	0.0
Land held for development	0.0	0.0
Land held for sale	0.0	0.0
Rental properties	2,710.4	2,902.4
Total inventories	2,710.4	2,902.4	2,708.4
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(42.2)	(14.7)
Property and equipment, net	0.6	1.1
Other Assets	38.9	74.5
Goodwill	0.0	0.0
Total assets	2,851.0	3,123.1
Liabilities
Accounts payable	230.6	474.2
Accrued expenses and other liabilities	34.7	67.8
Notes payable	600.0	750.7
Total liabilities	865.3	1,292.7
Revenues:
Revenues	1,640.4	1,685.1	2,605.5
Cost of sales:
Inventory and land option charges	7.3	5.8	6.7
Cost of sales	1,340.7	1,321.7	1,893.5
Selling, general and administrative expense	245.2	236.2	290.2
Other (income) expense (3)	115.5	101.5	102.4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	170.0	228.7	524.2
Depreciation and amortization	2.0	2.4	2.4
Cash provided by (used in) operating activities	105.5	(231.0)	739.2
Forestar Group [Member]
Assets
Cash and cash equivalents	379.2	481.2
Restricted cash	0.0	0.0
Inventories:
Construction in progress and finished homes	0.0	0.0
Residential land and lots — developed and under development	2,465.1	2,126.1
Land held for development	180.0	140.1
Land held for sale	0.0	0.0
Rental properties	0.0	0.0
Total inventories	2,645.1	2,266.2	1,790.3
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	0.0	0.0
Property and equipment, net	8.1	7.1
Other Assets	104.6	85.6
Goodwill	0.0	0.0
Total assets	3,137.0	2,840.1
Liabilities
Accounts payable	71.0	85.9
Accrued expenses and other liabilities	494.3	452.8
Notes payable	802.8	706.4
Total liabilities	1,368.1	1,245.1
Revenues:
Revenues	1,662.4	1,509.4	1,436.9
Cost of sales:
Inventory and land option charges	7.2	4.1	24.0
Cost of sales	1,298.9	1,150.0	1,132.9
Selling, general and administrative expense	154.4	118.5	97.7
Other (income) expense (3)	10.2	29.2	15.3
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	219.3	270.1	221.6
Depreciation and amortization	3.5	3.0	3.0
Cash provided by (used in) operating activities	(197.7)	(158.6)	364.1
Financial Services [Member]
Assets
Cash and cash equivalents	244.5	242.3
Restricted cash	19.9	20.6
Inventories:
Construction in progress and finished homes	0.0	0.0
Residential land and lots — developed and under development	0.0	0.0
Land held for development	0.0	0.0
Land held for sale	0.0	0.0
Rental properties	0.0	0.0
Total inventories	0.0	0.0
Mortgage loans held for sale	2,566.5	2,477.5
Deferred income taxes, net	0.0	0.0
Property and equipment, net	4.3	4.0
Other Assets	220.6	212.3
Goodwill	0.0	0.0
Total assets	3,055.8	2,956.7
Liabilities
Accounts payable	0.7	0.8
Accrued expenses and other liabilities	294.7	234.6
Notes payable	1,408.3	1,533.8
Total liabilities	1,703.7	1,769.2
Revenues:
Revenues	841.2	882.5	801.5
Cost of sales:
Inventory and land option charges	0.0	0.0	0.0
Cost of sales	0.0	0.0	0.0
Selling, general and administrative expense	651.4	672.4	594.9
Other (income) expense (3)	88.9	101.1	76.7
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	278.7	311.2	283.3
Depreciation and amortization	1.8	1.8	2.1
Cash provided by (used in) operating activities	173.2	281.6	13.2
Eliminations and Other
Assets
Cash and cash equivalents	10.4	12.3
Restricted cash	0.0	0.0
Inventories:
Construction in progress and finished homes	(95.2)	(110.3)
Residential land and lots — developed and under development	(282.4)	(189.7)
Land held for development	0.0	0.0
Land held for sale	0.0	0.0
Rental properties	(7.1)	3.6
Total inventories	(384.7)	(296.4)	(281.2)
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(39.0)	(29.4)
Property and equipment, net	22.9	18.6
Other Assets	89.0	(31.3)
Goodwill	29.2	29.2
Total assets	(272.2)	(297.0)
Liabilities
Accounts payable	(97.2)	(261.5)
Accrued expenses and other liabilities	(404.2)	(290.5)
Notes payable	0.0	0.0
Total liabilities	(501.4)	(552.0)
Revenues:
Revenues	(1,409.1)	(1,237.4)	(1,126.7)
Cost of sales:
Inventory and land option charges	(0.6)	0.0	(11.1)
Cost of sales	(1,364.6)	(1,266.7)	(1,232.2)
Selling, general and administrative expense	17.9	19.1	26.1
Other (income) expense (3)	(0.6)	9.4	(60.1)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(63.0)	19.6	19.3
Depreciation and amortization	0.6	0.5	20.1
Cash provided by (used in) operating activities	(67.7)	58.8	109.2
Northwest | Home Building
Inventories:
Total inventories	1,891.8	1,935.2	1,907.5
Goodwill	2.2	2.2
Revenues:
Revenues	2,686.2	2,761.7	2,582.4
Cost of sales:
Inventory and land option charges	3.8	4.4	6.6
Cost of sales	2,079.7	2,140.4	2,017.3
Selling, general and administrative expense	220.0	211.1	182.2
Other (income) expense (3)	9.2	10.6	8.2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	395.7	420.8	391.1
Southwest [Member] | Home Building
Inventories:
Total inventories	3,068.5	3,278.9	3,133.0
Goodwill	0.0	0.0
Revenues:
Revenues	4,595.3	4,914.7	4,282.8
Cost of sales:
Inventory and land option charges	16.7	12.7	11.3
Cost of sales	3,732.0	3,875.3	3,491.3
Selling, general and administrative expense	361.9	354.1	315.3
Other (income) expense (3)	15.7	18.2	13.1
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	517.1	703.5	489.3
South Central [Member] | Home Building
Inventories:
Total inventories	3,931.9	3,728.0	3,810.5
Goodwill	15.9	15.9
Revenues:
Revenues	6,899.3	7,652.1	7,612.6
Cost of sales:
Inventory and land option charges	36.7	11.4	7.6
Cost of sales	5,397.4	5,784.9	5,739.9
Selling, general and administrative expense	558.3	557.0	500.9
Other (income) expense (3)	21.0	21.2	16.5
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	964.6	1,331.4	1,388.3
Southeast [Member] | Home Building
Inventories:
Total inventories	4,061.8	4,284.5	3,958.5
Goodwill	6.0	6.0
Revenues:
Revenues	6,971.2	8,876.8	8,760.8
Cost of sales:
Inventory and land option charges	45.4	18.4	14.6
Cost of sales	5,564.5	6,824.8	6,495.0
Selling, general and administrative expense	587.8	634.4	574.7
Other (income) expense (3)	21.0	23.8	20.0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	839.9	1,441.4	1,711.1
East [Member] | Home Building
Inventories:
Total inventories	4,397.7	3,978.2	3,024.7
Goodwill	60.5	60.5
Revenues:
Revenues	6,138.0	6,073.1	5,325.3
Cost of sales:
Inventory and land option charges	29.2	11.9	8.4
Cost of sales	4,802.1	4,547.3	4,001.3
Selling, general and administrative expense	522.1	484.6	399.5
Other (income) expense (3)	20.2	18.4	11.2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	834.0	1,059.6	935.7
North | Home Building
Inventories:
Total inventories	2,637.6	2,551.2	2,078.0
Goodwill	49.7	49.7
Revenues:
Revenues	4,225.5	3,683.4	3,179.3
Cost of sales:
Inventory and land option charges	12.4	10.1	12.2
Cost of sales	3,283.5	2,888.3	2,571.0
Selling, general and administrative expense	373.0	312.1	267.3
Other (income) expense (3)	14.6	15.4	9.8
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	583.6	498.4	350.8
Corporate, Non-Segment [Member] | Home Building
Inventories:
Total inventories	327.2	275.0	243.6
Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31,432.0	33,903.6	31,641.0
Cost of sales:
Cost of Product and Service Sold	24,437.6	25,689.2	23,952.8
Home Building | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31,432.0	33,903.6	31,641.0
Cost of sales:
Cost of Product and Service Sold	24,664.9	25,952.1	24,201.3
Home Building | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Home Building | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Home Building | Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Home Building | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	(227.3)	(262.9)	(248.5)
Home Building | Northwest | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	2,685.7	2,744.6	2,574.1
Cost of sales:
Cost of Product and Service Sold	2,075.7	2,121.2	2,003.6
Home Building | Southwest [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	4,573.7	4,913.3	4,246.7
Cost of sales:
Cost of Product and Service Sold	3,695.4	3,862.5	3,451.2
Home Building | South Central [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	6,885.4	7,639.6	7,598.1
Cost of sales:
Cost of Product and Service Sold	5,350.7	5,765.4	5,721.6
Home Building | Southeast [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	6,939.4	8,853.4	8,756.5
Cost of sales:
Cost of Product and Service Sold	5,510.1	6,790.5	6,485.5
Home Building | East [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	6,131.1	6,070.9	5,323.9
Cost of sales:
Cost of Product and Service Sold	4,768.1	4,534.8	3,992.7
Home Building | North | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	4,216.7	3,681.8	3,141.7
Cost of sales:
Cost of Product and Service Sold	3,264.9	2,877.7	2,546.7
Land [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	336.8	330.2	412.4
Cost of sales:
Cost of Product and Service Sold	209.3	196.1	202.8
Land [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	83.5	58.2	102.2
Cost of sales:
Cost of Product and Service Sold	50.1	40.0	53.8
Land [Member] | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Land [Member] | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,662.4	1,509.4	1,436.9
Cost of sales:
Cost of Product and Service Sold	1,291.7	1,145.9	1,108.9
Land [Member] | Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Land [Member] | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	(1,409.1)	(1,237.4)	(1,126.7)
Cost of sales:
Cost of Product and Service Sold	(1,132.5)	(989.8)	(959.9)
Land [Member] | Northwest | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.5	17.1	8.3
Cost of sales:
Cost of Product and Service Sold	0.2	14.8	7.1
Land [Member] | Southwest [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	21.6	1.4	36.1
Cost of sales:
Cost of Product and Service Sold	19.9	0.1	28.8
Land [Member] | South Central [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	13.9	12.5	14.5
Cost of sales:
Cost of Product and Service Sold	10.0	8.1	10.7
Land [Member] | Southeast [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31.8	23.4	4.3
Cost of sales:
Cost of Product and Service Sold	9.0	15.9	(5.1)
Land [Member] | East [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	6.9	2.2	1.4
Cost of sales:
Cost of Product and Service Sold	4.8	0.6	0.2
Land [Member] | North | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	8.8	1.6	37.6
Cost of sales:
Cost of Product and Service Sold	6.2	0.5	12.1
Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,640.4	1,685.1	2,605.5
Cost of sales:
Cost of Product and Service Sold	1,329.2	1,301.9	1,874.1
Rental | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Rental | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,640.4	1,685.1	2,605.5
Cost of sales:
Cost of Product and Service Sold	1,333.4	1,315.9	1,886.8
Rental | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Rental | Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	0.0	0.0	0.0
Rental | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Product and Service Sold	(4.2)	(14.0)	(12.7)
Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	841.2	882.5	801.5
Financial Services [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Financial Services [Member] | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Financial Services [Member] | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Financial Services [Member] | Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	841.2	882.5	801.5
Financial Services [Member] | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	$ 0.0	$ 0.0	$ 0.0