Segment Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Assets
Cash and cash equivalents	$ 3,873.6	$ 2,540.5
Restricted cash	26.5	32.4
Inventories:
Construction in progress and finished homes	9,001.4	9,798.2
Residential land and lots — developed and under development	10,621.9	9,173.1
Land held for development	50.0	110.8
Land held for sale	8.7	29.4
Rental properties	2,691.3	2,544.2
Total inventories	22,373.3	21,655.7
Mortgage loans held for sale	2,519.9	2,386.0
Deferred income taxes, net	187.2	141.1
Property and equipment, net	445.4	471.6
Other Assets	2,993.0	2,960.3
Goodwill	163.5	163.5
Total assets	32,582.4	30,351.1
Liabilities
Accounts payable	1,246.2	1,360.3
Accrued expenses and other liabilities	3,103.8	3,138.3
Notes payable	5,094.5	6,066.9
Total liabilities	9,444.5	10,565.5
Revenues:
Revenues	35,460.4	33,480.0	$ 27,774.2
Cost of sales:
Inventory and land option charges	80.3	70.4	28.6
Cost of sales	26,110.0	22,975.9	19,899.2
Selling, general and administrative expense	3,248.8	2,933.7	2,556.2
Gain on sale of assets	0.0	0.0	(14.0)
Loss on extinguishment of debt	0.0	0.0	18.1
Other (income) expense	(213.1)	(59.3)	(41.6)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	6,314.7	7,629.7	5,356.3
Depreciation and amortization	91.6	81.4	82.1
Cash provided by (used in) operating activities	4,304.1	561.8	534.4
Home Building
Assets
Cash and cash equivalents	2,920.2	2,040.7
Restricted cash	6.5	11.3
Inventories:
Construction in progress and finished homes	9,134.3	9,951.5
Residential land and lots — developed and under development	8,992.3	7,322.5
Land held for development	20.5	21.0
Land held for sale	8.7	29.4
Rental properties	0.0	0.0
Total inventories	18,155.8	17,324.4
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	229.8	146.3
Property and equipment, net	415.0	361.8
Other Assets	2,838.5	2,266.5
Goodwill	134.3	134.3
Total assets	24,700.1	22,285.3
Liabilities
Accounts payable	1,033.7	1,149.1
Accrued expenses and other liabilities	2,585.5	2,365.7
Notes payable	2,329.9	2,942.6
Total liabilities	5,949.1	6,457.4
Revenues:
Revenues	31,743.2	31,923.1	26,577.6
Cost of sales:
Inventory and land option charges	60.7	57.2	24.9
Cost of sales	24,315.8	22,811.9	19,829.5
Selling, general and administrative expense	2,239.9	2,186.7	1,945.6
Gain on sale of assets			0.0
Loss on extinguishment of debt			0.0
Other (income) expense	(78.8)	(16.4)	(10.3)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	5,266.3	6,940.9	4,812.8
Depreciation and amortization	64.0	62.5	63.1
Cash provided by (used in) operating activities	3,078.4	1,916.7	1,239.8
Rental
Assets
Cash and cash equivalents	136.1	109.9
Restricted cash	3.3	1.4
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	2,708.4	2,572.1
Total inventories	2,708.4	2,572.1
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(19.9)	(7.1)
Property and equipment, net	2.4	2.0
Other Assets	29.8	18.4
Goodwill	0.0	0.0
Total assets	2,860.1	2,696.7
Liabilities
Accounts payable	698.6	233.6
Accrued expenses and other liabilities	43.2	25.0
Notes payable	400.0	800.0
Total liabilities	1,141.8	1,058.6
Revenues:
Revenues	2,605.5	510.2	267.8
Cost of sales:
Inventory and land option charges	6.7	0.8	0.7
Cost of sales	1,893.5	244.2	161.5
Selling, general and administrative expense	290.2	91.1	44.6
Gain on sale of assets			0.0
Loss on extinguishment of debt			0.0
Other (income) expense	(102.4)	(27.1)	(24.8)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	524.2	202.0	86.5
Depreciation and amortization	2.4	1.0	5.1
Cash provided by (used in) operating activities	739.2	(1,391.0)	(410.0)
Forestar Group [Member]
Assets
Cash and cash equivalents	616.0	264.8
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	1,760.8	1,932.6
Land held for development	29.5	89.8
Land held for sale	0.0	0.0
Rental properties	0.0	0.0
Total inventories	1,790.3	2,022.4
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	0.0	0.0
Property and equipment, net	5.9	5.7
Other Assets	58.5	50.1
Goodwill	0.0	0.0
Total assets	2,470.7	2,343.0
Liabilities
Accounts payable	68.4	72.2
Accrued expenses and other liabilities	337.4	365.4
Notes payable	695.0	706.0
Total liabilities	1,100.8	1,143.6
Revenues:
Revenues	1,436.9	1,519.1	1,325.8
Cost of sales:
Inventory and land option charges	24.0	12.4	3.0
Cost of sales	1,132.9	1,195.1	1,096.6
Selling, general and administrative expense	97.7	93.6	68.4
Gain on sale of assets			(2.5)
Loss on extinguishment of debt			18.1
Other (income) expense	(15.3)	(5.4)	(1.4)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	221.6	235.8	146.6
Depreciation and amortization	3.0	2.7	2.2
Cash provided by (used in) operating activities	364.1	108.7	(303.1)
Financial Services [Member]
Assets
Cash and cash equivalents	189.1	103.3
Restricted cash	16.7	19.7
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	2,519.9	2,386.0
Deferred income taxes, net	0.0	0.0
Property and equipment, net	4.1	4.3
Other Assets	250.3	492.5
Goodwill	0.0	0.0
Total assets	2,980.1	3,005.8
Liabilities
Accounts payable	0.1	0.2
Accrued expenses and other liabilities	280.4	596.2
Notes payable	1,669.6	1,618.3
Total liabilities	1,950.1	2,214.7
Revenues:
Revenues	801.5	795.0	823.6
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	594.9	547.6	488.3
Gain on sale of assets			0.0
Loss on extinguishment of debt			0.0
Other (income) expense	(76.7)	(43.2)	(29.3)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	283.3	290.6	364.6
Depreciation and amortization	2.1	1.9	1.7
Cash provided by (used in) operating activities	13.2	(10.5)	(195.8)
Eliminations and Other
Assets
Cash and cash equivalents	12.2	21.8
Restricted cash	0.0	0.0
Inventories:
Construction in progress and finished homes	(132.9)	(153.3)
Residential land and lots — developed and under development	(131.2)	(82.0)
Land held for development	0.0	0.0
Land held for sale	0.0	0.0
Rental properties	(17.1)	(27.9)
Total inventories	(281.2)	(263.2)
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(22.7)	1.9
Property and equipment, net	18.0	97.8
Other Assets	(184.1)	132.8
Goodwill	29.2	29.2
Total assets	(428.6)	20.3
Liabilities
Accounts payable	(554.6)	(94.8)
Accrued expenses and other liabilities	(142.7)	(214.0)
Notes payable	0.0	0.0
Total liabilities	(697.3)	(308.8)
Revenues:
Revenues	(1,126.7)	(1,267.4)	(1,220.6)
Cost of sales:
Inventory and land option charges	(11.1)	0.0	0.0
Cost of sales	(1,232.2)	(1,275.3)	(1,188.4)
Selling, general and administrative expense	26.1	14.7	9.3
Gain on sale of assets			(11.5)
Loss on extinguishment of debt			0.0
Other (income) expense	60.1	32.8	24.2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	19.3	(39.6)	(54.2)
Depreciation and amortization	20.1	13.3	10.0
Cash provided by (used in) operating activities	109.2	(62.1)	203.5
Northwest | Home Building
Inventories:
Total inventories	1,907.5	1,802.2
Goodwill	2.2	2.2
Revenues:
Revenues	2,582.4	2,658.4	2,516.6
Cost of sales:
Inventory and land option charges	6.6	7.0	0.6
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	391.1	560.8	510.8
Southwest [Member] | Home Building
Inventories:
Total inventories	3,133.0	2,801.7
Goodwill	0.0	0.0
Revenues:
Revenues	4,282.8	4,840.7	4,071.0
Cost of sales:
Inventory and land option charges	11.3	6.3	3.0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	489.3	968.3	653.1
South Central [Member] | Home Building
Inventories:
Total inventories	3,810.5	3,931.7
Goodwill	15.9	15.9
Revenues:
Revenues	7,612.6	8,192.3	6,111.2
Cost of sales:
Inventory and land option charges	7.6	9.9	5.3
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,388.3	1,910.7	1,150.2
Southeast [Member] | Home Building
Inventories:
Total inventories	3,958.5	4,091.1
Goodwill	6.0	6.0
Revenues:
Revenues	8,760.8	7,951.2	7,079.6
Cost of sales:
Inventory and land option charges	14.6	13.5	10.2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,711.1	1,918.5	1,371.9
East [Member] | Home Building
Inventories:
Total inventories	3,024.7	2,542.7
Goodwill	60.5	60.5
Revenues:
Revenues	5,325.3	5,318.1	4,459.0
Cost of sales:
Inventory and land option charges	8.4	12.1	2.4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	935.7	1,126.3	795.1
North | Home Building
Inventories:
Total inventories	2,078.0	1,935.7
Goodwill	49.7	49.7
Revenues:
Revenues	3,179.3	2,962.4	2,340.2
Cost of sales:
Inventory and land option charges	12.2	8.4	3.4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	350.8	456.3	331.7
Corporate, Non-Segment [Member] | Home Building
Inventories:
Total inventories	243.6	219.3
Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31,641.0	31,861.7	26,502.6
Cost of sales:
Cost of Goods and Services Sold	23,952.8	22,517.7	19,608.3
Home Building | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31,641.0	31,861.7	26,502.6
Cost of sales:
Cost of Goods and Services Sold	24,201.3	22,715.6	19,748.4
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	(248.5)	(197.9)	(140.1)
Land [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	412.4	313.1	212.0
Cost of sales:
Cost of Goods and Services Sold	202.8	149.5	119.3
Land [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	102.2	61.4	75.0
Cost of sales:
Cost of Goods and Services Sold	53.8	39.1	56.2
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	1,436.9	1,519.1	1,325.8
Cost of sales:
Cost of Goods and Services Sold	1,108.9	1,182.7	1,093.6
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	(1,126.7)	(1,267.4)	(1,188.8)
Cost of sales:
Cost of Goods and Services Sold	(959.9)	(1,072.3)	(1,030.5)
Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	2,605.5	510.2	236.0
Cost of sales:
Cost of Goods and Services Sold	1,874.1	238.3	143.0
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	2,605.5	510.2	267.8
Cost of sales:
Cost of Goods and Services Sold	1,886.8	243.4	160.8
Rental | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Cost of sales:
Cost of 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	(31.8)
Cost of sales:
Cost of Goods and Services Sold	(12.7)	(5.1)	(17.8)
Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	801.5	795.0	823.6
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	801.5	795.0	823.6
Financial Services [Member] | Eliminations and Other
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	$ 0.0	$ 0.0	$ 0.0