Notes Payable - Terms (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Notes payable, carrying value	$ 5,917.7	$ 5,094.5
Home Building Consolidated
Debt Instrument [Line Items]
Line of credit, amount outstanding	0.0	0.0
Notes payable, carrying value	2,926.8	2,329.9
Rental
Debt Instrument [Line Items]
Line of credit, amount outstanding	745.0	400.0
Notes payable, carrying value	750.7	400.0
SeniorNoteFortyTwo [Member] \| Home Building Consolidated
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Instrument, Maturity Date	Oct. 15, 2024
Debt Instrument, Call Feature	Yes
Debt Instrument, Interest Rate, Effective Percentage	2.70%
Senior notes, stated interest rate	2.50%
Notes payable, carrying value	$ 500.0	499.0
SeniorNoteFortyFour \| Home Building Consolidated
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Instrument, Maturity Date	Oct. 15, 2025
Debt Instrument, Call Feature	Yes
Debt Instrument, Interest Rate, Effective Percentage	2.80%
Senior notes, stated interest rate	2.60%
Notes payable, carrying value	$ 499.0	498.0
SeniorNoteFortySIx \| Home Building Consolidated
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 600.0
Debt Instrument, Maturity Date	Oct. 15, 2026
Debt Instrument, Call Feature	Yes
Debt Instrument, Interest Rate, Effective Percentage	1.50%
Senior notes, stated interest rate	1.30%
Notes payable, carrying value	$ 597.7	596.6
Senior Note Forty Five [Member] \| Home Building Consolidated
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Instrument, Maturity Date	Oct. 15, 2027
Debt Instrument, Call Feature	Yes
Debt Instrument, Interest Rate, Effective Percentage	1.60%
Senior notes, stated interest rate	1.40%
Notes payable, carrying value	$ 497.4	496.5
Senior Notes [Member] \| Home Building Consolidated
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Senior Note Forty Eight \| Home Building Consolidated
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 700.0
Debt Instrument, Maturity Date	Oct. 15, 2034
Debt Instrument, Call Feature	Yes
Debt Instrument, Interest Rate, Effective Percentage	5.20%
Senior notes, stated interest rate	5.00%
Notes payable, carrying value	$ 686.5	$ 0.0

Description of a feature that permits the issuer of the debt to repay or convert it before the stated maturity date (early retirement date). The description may include such items as the call price, the period that the issuer can call the debt, including the earliest call date, and other significant terms of the call feature, which may include the debt holders' ability to convert the debt to equity if the call option is exercised and contingent events that trigger the issuer's ability to call the debt.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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