Segment Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Assets
Cash and cash equivalents	$ 4,516.4	$ 3,873.6
Restricted cash	27.6	26.5
Inventories:
Construction in progress and finished homes	8,875.8	9,001.4
Residential land and lots — developed and under development	12,948.1	10,621.9
Land held for development	160.6	50.0
Land held for sale	12.7	8.7
Rental properties	2,906.0	2,691.3
Total inventories	24,903.2	22,373.3
Mortgage loans held for sale	2,477.5	2,519.9
Deferred income taxes, net	167.5	187.2
Property and equipment, net	531.0	445.4
Other Assets	3,317.6	2,993.0
Goodwill	163.5	163.5
Total assets	36,104.3	32,582.4
Liabilities
Accounts payable	1,345.5	1,246.2
Accrued expenses and other liabilities	3,016.7	3,103.8
Notes payable	5,917.7	5,094.5
Total liabilities	10,279.9	9,444.5
Revenues:
Revenues	36,801.4	35,460.4	$ 33,480.0
Cost of sales:
Inventory and land option charges	78.8	80.3	70.4
Cost of sales	27,266.0	26,110.0	22,975.9
Selling, general and administrative expense	3,599.5	3,248.8	2,933.7
Other (income) expense	(348.8)	(213.1)	(59.3)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	6,284.7	6,314.7	7,629.7
Depreciation and amortization	87.1	91.6	81.4
Cash provided by (used in) operating activities	2,189.8	4,304.1	561.8
Home Building
Assets
Cash and cash equivalents	3,623.0	2,920.2
Restricted cash	4.8	6.5
Inventories:
Construction in progress and finished homes	8,986.1	9,134.3
Residential land and lots — developed and under development	11,011.7	8,992.3
Land held for development	20.5	20.5
Land held for sale	12.7	8.7
Rental properties	0.0	0.0
Total inventories	20,031.0	18,155.8
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	211.6	229.8
Property and equipment, net	500.2	415.0
Other Assets	2,976.5	2,838.5
Goodwill	134.3	134.3
Total assets	27,481.4	24,700.1
Liabilities
Accounts payable	1,046.1	1,033.7
Accrued expenses and other liabilities	2,552.0	2,585.5
Notes payable	2,926.8	2,329.9
Total liabilities	6,524.9	5,949.1
Revenues:
Revenues	33,961.8	31,743.2	31,923.1
Cost of sales:
Inventory and land option charges	68.9	60.7	57.2
Cost of sales	26,061.0	24,315.8	22,811.9
Selling, general and administrative expense	2,553.3	2,239.9	2,186.7
Other (income) expense	(107.6)	(78.8)	(16.4)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	5,455.1	5,266.3	6,940.9
Depreciation and amortization	79.4	64.0	62.5
Cash provided by (used in) operating activities	2,239.0	3,078.4	1,916.7
Rental
Assets
Cash and cash equivalents	157.6	136.1
Restricted cash	2.2	3.3
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	2,902.4	2,708.4
Total inventories	2,902.4	2,708.4
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(14.7)	(19.9)
Property and equipment, net	1.1	2.4
Other Assets	74.5	29.8
Goodwill	0.0	0.0
Total assets	3,123.1	2,860.1
Liabilities
Accounts payable	474.2	698.6
Accrued expenses and other liabilities	67.8	43.2
Notes payable	750.7	400.0
Total liabilities	1,292.7	1,141.8
Revenues:
Revenues	1,685.1	2,605.5	510.2
Cost of sales:
Inventory and land option charges	5.8	6.7	0.8
Cost of sales	1,321.7	1,893.5	244.2
Selling, general and administrative expense	236.2	290.2	91.1
Other (income) expense	(101.5)	(102.4)	(27.1)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	228.7	524.2	202.0
Depreciation and amortization	2.4	2.4	1.0
Cash provided by (used in) operating activities	(231.0)	739.2	(1,391.0)
Forestar Group [Member]
Assets
Cash and cash equivalents	481.2	616.0
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	2,126.1	1,760.8
Land held for development	140.1	29.5
Land held for sale	0.0	0.0
Rental properties	0.0	0.0
Total inventories	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	7.1	5.9
Other Assets	85.6	58.5
Goodwill	0.0	0.0
Total assets	2,840.1	2,470.7
Liabilities
Accounts payable	85.9	68.4
Accrued expenses and other liabilities	452.8	337.4
Notes payable	706.4	695.0
Total liabilities	1,245.1	1,100.8
Revenues:
Revenues	1,509.4	1,436.9	1,519.1
Cost of sales:
Inventory and land option charges	4.1	24.0	12.4
Cost of sales	1,150.0	1,132.9	1,195.1
Selling, general and administrative expense	118.5	97.7	93.6
Other (income) expense	(29.2)	(15.3)	(5.4)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	270.1	221.6	235.8
Depreciation and amortization	3.0	3.0	2.7
Cash provided by (used in) operating activities	(158.6)	364.1	108.7
Financial Services [Member]
Assets
Cash and cash equivalents	242.3	189.1
Restricted cash	20.6	16.7
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	2,477.5	2,519.9
Deferred income taxes, net	0.0	0.0
Property and equipment, net	4.0	4.1
Other Assets	212.3	250.3
Goodwill	0.0	0.0
Total assets	2,956.7	2,980.1
Liabilities
Accounts payable	0.8	0.1
Accrued expenses and other liabilities	234.6	280.4
Notes payable	1,533.8	1,669.6
Total liabilities	1,769.2	1,950.1
Revenues:
Revenues	882.5	801.5	795.0
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	672.4	594.9	547.6
Other (income) expense	(101.1)	(76.7)	(43.2)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	311.2	283.3	290.6
Depreciation and amortization	1.8	2.1	1.9
Cash provided by (used in) operating activities	281.6	13.2	(10.5)
Eliminations and Other
Assets
Cash and cash equivalents	12.3	12.2
Restricted cash	0.0	0.0
Inventories:
Construction in progress and finished homes	(110.3)	(132.9)
Residential land and lots — developed and under development	(189.7)	(131.2)
Land held for development	0.0	0.0
Land held for sale	0.0	0.0
Rental properties	3.6	(17.1)
Total inventories	(296.4)	(281.2)
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(29.4)	(22.7)
Property and equipment, net	18.6	18.0
Other Assets	(31.3)	(184.1)
Goodwill	29.2	29.2
Total assets	(297.0)	(428.6)
Liabilities
Accounts payable	(261.5)	(554.6)
Accrued expenses and other liabilities	(290.5)	(142.7)
Notes payable	0.0	0.0
Total liabilities	(552.0)	(697.3)
Revenues:
Revenues	(1,237.4)	(1,126.7)	(1,267.4)
Cost of sales:
Inventory and land option charges	0.0	(11.1)	0.0
Cost of sales	(1,266.7)	(1,232.2)	(1,275.3)
Selling, general and administrative expense	19.1	26.1	14.7
Other (income) expense	(9.4)	60.1	32.8
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	19.6	19.3	(39.6)
Depreciation and amortization	0.5	20.1	13.3
Cash provided by (used in) operating activities	58.8	109.2	(62.1)
Northwest | Home Building
Inventories:
Total inventories	1,935.2	1,907.5
Goodwill	2.2	2.2
Revenues:
Revenues	2,761.7	2,582.4	2,658.4
Cost of sales:
Inventory and land option charges	4.4	6.6	7.0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	420.8	391.1	560.8
Southwest [Member] | Home Building
Inventories:
Total inventories	3,278.9	3,133.0
Goodwill	0.0	0.0
Revenues:
Revenues	4,914.7	4,282.8	4,840.7
Cost of sales:
Inventory and land option charges	12.7	11.3	6.3
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	703.5	489.3	968.3
South Central [Member] | Home Building
Inventories:
Total inventories	3,728.0	3,810.5
Goodwill	15.9	15.9
Revenues:
Revenues	7,652.1	7,612.6	8,192.3
Cost of sales:
Inventory and land option charges	11.4	7.6	9.9
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,331.4	1,388.3	1,910.7
Southeast [Member] | Home Building
Inventories:
Total inventories	4,284.5	3,958.5
Goodwill	6.0	6.0
Revenues:
Revenues	8,876.8	8,760.8	7,951.2
Cost of sales:
Inventory and land option charges	18.4	14.6	13.5
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,441.4	1,711.1	1,918.5
East [Member] | Home Building
Inventories:
Total inventories	3,978.2	3,024.7
Goodwill	60.5	60.5
Revenues:
Revenues	6,073.1	5,325.3	5,318.1
Cost of sales:
Inventory and land option charges	11.9	8.4	12.1
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,059.6	935.7	1,126.3
North | Home Building
Inventories:
Total inventories	2,551.2	2,078.0
Goodwill	49.7	49.7
Revenues:
Revenues	3,683.4	3,179.3	2,962.4
Cost of sales:
Inventory and land option charges	10.1	12.2	8.4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	498.4	350.8	456.3
Corporate, Non-Segment [Member] | Home Building
Inventories:
Total inventories	275.0	243.6
Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	33,903.6	31,641.0	31,861.7
Cost of sales:
Cost of Goods and Services Sold	25,689.2	23,952.8	22,517.7
Home Building | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	33,903.6	31,641.0	31,861.7
Cost of sales:
Cost of Goods and Services Sold	25,952.1	24,201.3	22,715.6
Home Building | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Goods and Services 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 Goods and Services 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 Goods and Services 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 Goods and Services Sold	(262.9)	(248.5)	(197.9)
Land [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	330.2	412.4	313.1
Cost of sales:
Cost of Goods and Services Sold	196.1	202.8	149.5
Land [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	58.2	102.2	61.4
Cost of sales:
Cost of Goods and Services Sold	40.0	53.8	39.1
Land [Member] | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Goods and Services Sold	0.0	0.0	0.0
Land [Member] | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,509.4	1,436.9	1,519.1
Cost of sales:
Cost of Goods and Services Sold	1,145.9	1,108.9	1,182.7
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 Goods and Services Sold	0.0	0.0	0.0
Land [Member] | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	(1,237.4)	(1,126.7)	(1,267.4)
Cost of sales:
Cost of Goods and Services Sold	(989.8)	(959.9)	(1,072.3)
Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,685.1	2,605.5	510.2
Cost of sales:
Cost of Goods and Services Sold	1,301.9	1,874.1	238.3
Rental | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Goods and Services Sold	0.0	0.0	0.0
Rental | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,685.1	2,605.5	510.2
Cost of sales:
Cost of Goods and Services Sold	1,315.9	1,886.8	243.4
Rental | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of Goods and Services 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 Goods and Services 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 Goods and Services Sold	(14.0)	(12.7)	(5.1)
Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	882.5	801.5	795.0
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	882.5	801.5	795.0
Financial Services [Member] | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	$ 0.0	$ 0.0	$ 0.0