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Related Party Disclosures (Details) $ in Millions	9 Months Ended		12 Months Ended
Related Party Disclosures (Details) $ in Millions	Sep. 30, 2018 USD ($) a Lot	Sep. 30, 2017 USD ($)	Sep. 30, 2020 USD ($) Lot	Sep. 30, 2019 USD ($) a Lot
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot			60,500	38,300
Number of Lots Sold \| Lot	1,024		10,373	4,132
Income (Loss) from Equity Method Investments	$ 4.8	$ 10.9	$ 0.7	$ 0.5
Real estate			1,309.7	1,028.9
Due to Related Parties, Current			8.4	2.2
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Period Increase (Decrease)	(6.4)		2.3	4.0
Related Party Transaction, Purchases from Related Party	0.6		6.2	2.4
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	0.9		5.0	2.1
Related Party Transaction, Expenses from Transactions with Related Party	0.9		2.7	1.4
D.R. Horton, Inc. [Member] \| Contract Termination [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction				2.1
D.R. Horton, Inc. [Member] \| Reimbursement From Parent [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction				0.4
D.R. Horton, Inc. [Member] \| Reimbursement To Parent [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction			0.2
D.R. Horton, Inc. [Member] \| Deposits [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	21.2		27.0	34.5
D.R. Horton, Inc. [Member] \| Other Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	15.2		36.3	13.1
Residential Real Estate [Member] \| Real Estate
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 72.0		880.3	351.7
Land [Member]
Related Party Transaction [Line Items]
Real estate			$ 5.4	$ 17.1
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Lots Sold \| Lot	642		10,164	3,728
Revenue from Related Parties	$ 43.6		$ 859.7	$ 311.7
Related Party Transaction, Rate			16.00%
D.R. Horton, Inc. [Member] \| Equity Method Investments [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	37.50%
Area of Land \| a	40
Proceeds from Sale of Real Estate	$ 7.8
Income (Loss) from Equity Method Investments	$ 2.5
D.R. Horton, Inc. [Member] \| Land [Member]
Related Party Transaction [Line Items]
Number of Lots Sold \| Lot	79		143	290
Revenue from Related Parties	$ 2.0		$ 25.6	$ 10.9
D.R. Horton, Inc. [Member] \| Under Contract [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot			14,000	12,800
Related Party Transaction, Purchase Obligation from Parent			$ 1,022.2	$ 953.8
D.R. Horton, Inc. [Member] \| Under Contract [Member] \| Cash [Member]
Related Party Transaction [Line Items]
Related Party Deposit Liabilities			92.2	88.7
D.R. Horton, Inc. [Member] \| Under Contract [Member] \| Notes Payable, Other Payables [Member]
Related Party Transaction [Line Items]
Related Party Deposit Liabilities			$ 4.8	$ 0.0
D.R. Horton, Inc. [Member] \| Right of First Offer [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot			16,400	10,600
Other Customer [Member] \| Equity Method Investments [Member]
Related Party Transaction [Line Items]
Area of Land \| a				63
Proceeds from Sale of Real Estate				$ 44.2