Segment Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Assets
Cash and cash equivalents	$ 2,540.5	$ 3,210.4
Restricted cash	32.4	26.8
Inventories:
Construction in progress and finished homes	9,798.2	7,739.2
Residential land and lots — developed and under development	9,173.1	7,781.8
Land held for development	110.8	110.9
Land held for sale	29.4	25.4
Rental properties	2,544.2	821.8
Total inventories	21,655.7	16,479.1
Mortgage loans held for sale	2,386.0	2,027.3
Deferred income taxes, net	141.1	155.3
Property and equipment, net	471.6	392.9
Other Assets	2,960.3	1,560.6
Goodwill	163.5	163.5
Total assets	30,351.1	24,015.9
Liabilities
Accounts payable	1,360.3	1,177.0
Accrued expenses and other liabilities	3,138.3	2,210.3
Notes payable	6,066.9	5,412.4
Total liabilities	10,565.5	8,799.7
Revenues:
Revenues	33,480.0	27,774.2	$ 20,311.1
Cost of sales:
Inventory and land option charges	70.4	28.6	23.8
Cost of sales	22,975.9	19,899.2	15,373.2
Selling, general and administrative expense	2,933.7	2,556.2	2,047.8
Gain on sale of assets	0.0	(14.0)	(59.5)
Loss on extinguishment of debt	0.0	18.1	0.0
Other (income) expense	(59.3)	(41.6)	(33.4)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	7,629.7	5,356.3	2,983.0
Depreciation and amortization	81.4	82.1	90.6
Cash provided by (used in) operating activities	561.8	534.4	1,421.6
Intersegment Eliminations [Member]
Assets
Cash and cash equivalents	21.8	10.9
Restricted cash	0.0	0.0
Inventories:
Construction in progress and finished homes	(153.3)	(108.8)
Residential land and lots — developed and under development	(82.0)	(46.9)
Land held for development	0.0	0.0
Land held for sale	0.0	0.0
Rental properties	(27.9)	(19.1)
Total inventories	(263.2)	(174.8)
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	1.9	(3.9)
Property and equipment, net	97.8	82.6
Other Assets	132.8	(62.0)
Total assets	20.3	(118.0)
Liabilities
Accounts payable	(94.8)	0.0
Accrued expenses and other liabilities	(214.0)	(168.5)
Notes payable	0.0	(0.7)
Total liabilities	(308.8)	(169.2)
Revenues:
Revenues	(1,267.4)	(1,220.6)	(975.6)
Cost of sales:
Inventory and land option charges	0.0	0.0	0.0
Cost of sales	(1,275.3)	(1,188.4)	(896.5)
Selling, general and administrative expense	14.7	9.3	8.9
Gain on sale of assets		(11.5)	(59.4)
Loss on extinguishment of debt		0.0
Other (income) expense	32.8	24.2	17.0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(39.6)	(54.2)	(45.6)
Depreciation and amortization	13.3	10.0	6.5
Cash provided by (used in) operating activities	(62.1)	203.5	66.3
Home Building
Assets
Cash and cash equivalents	2,040.7	2,950.1
Restricted cash	11.3	8.4
Inventories:
Construction in progress and finished homes	9,951.5	7,848.0
Residential land and lots — developed and under development	7,322.5	6,004.0
Land held for development	21.0	30.4
Land held for sale	29.4	25.4
Rental properties	0.0	0.0
Total inventories	17,324.4	13,907.8
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	146.3	159.2
Property and equipment, net	361.8	303.3
Other Assets	2,266.5	1,468.7
Goodwill	134.3	134.3
Total assets	22,285.3	18,931.8
Liabilities
Accounts payable	1,149.1	1,073.7
Accrued expenses and other liabilities	2,365.7	1,941.3
Notes payable	2,942.6	3,214.0
Total liabilities	6,457.4	6,229.0
Revenues:
Revenues	31,923.1	26,577.6	19,641.5
Cost of sales:
Inventory and land option charges	57.2	24.9	22.9
Cost of sales	22,811.9	19,829.5	15,387.0
Selling, general and administrative expense	2,186.7	1,945.6	1,600.7
Gain on sale of assets		0.0	0.0
Loss on extinguishment of debt		0.0
Other (income) expense	(16.4)	(10.3)	(11.7)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	6,940.9	4,812.8	2,665.5
Depreciation and amortization	62.5	63.1	72.6
Cash provided by (used in) operating activities	1,916.7	1,239.8	1,888.4
Financial Services [Member]
Assets
Cash and cash equivalents	103.3	79.0
Restricted cash	19.7	18.0
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	2,386.0	2,027.3
Deferred income taxes, net	0.0	0.0
Property and equipment, net	4.3	3.5
Other Assets	492.5	107.6
Goodwill	0.0	0.0
Total assets	3,005.8	2,235.4
Liabilities
Accounts payable	0.2	0.0
Accrued expenses and other liabilities	596.2	88.6
Notes payable	1,618.3	1,494.6
Total liabilities	2,214.7	1,583.2
Revenues:
Revenues	795.0	823.6	584.9
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	547.6	488.3	364.7
Gain on sale of assets		0.0	0.0
Loss on extinguishment of debt		0.0
Other (income) expense	(43.2)	(29.3)	(25.0)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	290.6	364.6	245.2
Depreciation and amortization	1.9	1.7	1.6
Cash provided by (used in) operating activities	(10.5)	(195.8)	(292.8)
Forestar Group [Member]
Assets
Cash and cash equivalents	264.8	153.6
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	1,932.6	1,824.7
Land held for development	89.8	80.5
Land held for sale	0.0	0.0
Rental properties	0.0	0.0
Total inventories	2,022.4	1,905.2
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	0.0	0.0
Property and equipment, net	5.7	2.9
Other Assets	50.1	40.0
Goodwill	0.0	0.0
Total assets	2,343.0	2,101.7
Liabilities
Accounts payable	72.2	47.4
Accrued expenses and other liabilities	365.4	333.9
Notes payable	706.0	704.5
Total liabilities	1,143.6	1,085.8
Revenues:
Revenues	1,519.1	1,325.8	931.8
Cost of sales:
Inventory and land option charges	12.4	3.0	0.9
Cost of sales	1,195.1	1,096.6	813.7
Selling, general and administrative expense	93.6	68.4	45.7
Gain on sale of assets		(2.5)	(0.1)
Loss on extinguishment of debt		18.1
Other (income) expense	(5.4)	(1.4)	(5.6)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	235.8	146.6	78.1
Depreciation and amortization	2.7	2.2	4.9
Cash provided by (used in) operating activities	108.7	(303.1)	(168.5)
Forestar Group [Member] | Intersegment Eliminations [Member]
Inventories:
Goodwill	29.2	29.2
Rental
Assets
Cash and cash equivalents	109.9	16.8
Restricted cash	1.4	0.4
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	2,572.1	840.9
Total inventories	2,572.1	840.9
Mortgage loans held for sale	0.0	0.0
Deferred income taxes, net	(7.1)	0.0
Property and equipment, net	2.0	0.6
Other Assets	18.4	6.3
Goodwill	0.0	0.0
Total assets	2,696.7	865.0
Liabilities
Accounts payable	233.6	55.9
Accrued expenses and other liabilities	25.0	15.0
Notes payable	800.0	0.0
Total liabilities	1,058.6	70.9
Revenues:
Revenues	510.2	267.8	128.5
Cost of sales:
Inventory and land option charges	0.8	0.7	0.0
Cost of sales	244.2	161.5	69.0
Selling, general and administrative expense	91.1	44.6	27.8
Gain on sale of assets		0.0	0.0
Loss on extinguishment of debt		0.0
Other (income) expense	(27.1)	(24.8)	(8.1)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	202.0	86.5	39.8
Depreciation and amortization	1.0	5.1	5.0
Cash provided by (used in) operating activities	(1,391.0)	(410.0)	(71.8)
Northwest | Home Building
Inventories:
Total inventories	1,802.2	1,307.5
Goodwill	2.2	2.2
Revenues:
Revenues	2,658.4	2,516.6	1,953.4
Cost of sales:
Inventory and land option charges	7.0	0.6	1.3
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	560.8	510.8	264.5
Southwest [Member] | Home Building
Inventories:
Total inventories	2,801.7	2,445.6
Goodwill	0.0	0.0
Revenues:
Revenues	4,840.7	4,071.0	3,230.3
Cost of sales:
Inventory and land option charges	6.3	3.0	3.5
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	968.3	653.1	366.1
South Central [Member] | Home Building
Inventories:
Total inventories	3,931.7	3,479.3
Goodwill	15.9	15.9
Revenues:
Revenues	8,192.3	6,111.2	4,625.9
Cost of sales:
Inventory and land option charges	9.9	5.3	6.4
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,910.7	1,150.2	714.9
Southeast [Member] | Home Building
Inventories:
Total inventories	4,091.1	3,178.6
Goodwill	6.0	6.0
Revenues:
Revenues	7,951.2	7,079.6	4,871.5
Cost of sales:
Inventory and land option charges	13.5	10.2	5.9
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,918.5	1,371.9	709.5
East [Member] | Home Building
Inventories:
Total inventories	2,542.7	1,919.6
Goodwill	60.5	60.5
Revenues:
Revenues	5,318.1	4,459.0	3,410.1
Cost of sales:
Inventory and land option charges	12.1	2.4	3.0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	1,126.3	795.1	484.3
North | Home Building
Inventories:
Total inventories	1,935.7	1,368.9
Goodwill	49.7	49.7
Revenues:
Revenues	2,962.4	2,340.2	1,550.3
Cost of sales:
Inventory and land option charges	8.4	3.4	2.8
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	456.3	331.7	126.2
Corporate, Non-Segment [Member] | Home Building
Inventories:
Total inventories	219.3	208.3
Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31,861.7	26,502.6	19,560.8
Cost of sales:
Cost of Goods and Services Sold	22,517.7	19,608.3	15,247.2
Home Building | Intersegment Eliminations [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	(197.9)	(140.1)	(58.6)
Home Building | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	31,861.7	26,502.6	19,560.8
Cost of sales:
Cost of Goods and Services Sold	22,715.6	19,748.4	15,305.8
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 | 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 | 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]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	313.1	212.0	165.4
Cost of sales:
Cost of Goods and Services Sold	149.5	119.3	102.2
Land [Member] | Intersegment Eliminations [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	(1,267.4)	(1,188.8)	(847.1)
Cost of sales:
Cost of Goods and Services Sold	(1,072.3)	(1,030.5)	(768.9)
Land [Member] | Home Building
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	61.4	75.0	80.7
Cost of sales:
Cost of Goods and Services Sold	39.1	56.2	58.3
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] | Forestar Group [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	1,519.1	1,325.8	931.8
Cost of sales:
Cost of Goods and Services Sold	1,182.7	1,093.6	812.8
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
Financial Services [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	795.0	823.6	584.9
Financial Services [Member] | Intersegment Eliminations [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	0.0	0.0
Financial Services [Member] | Home Building
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	795.0	823.6	584.9
Financial Services [Member] | Forestar Group [Member]
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
Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	510.2	236.0	0.0
Cost of sales:
Cost of Goods and Services Sold	238.3	143.0	0.0
Rental | Intersegment Eliminations [Member]
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	0.0	(31.8)	(128.5)
Cost of sales:
Cost of Goods and Services Sold	(5.1)	(17.8)	(69.0)
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 | 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 | 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 | Rental
Revenues:
Revenue from Contract with Customer, Including Assessed Tax	510.2	267.8	128.5
Cost of sales:
Cost of Goods and Services Sold	$ 243.4	$ 160.8	$ 69.0