Notes Payable - Financial Services Textuals (Details) - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Notes payable	$ 6,518.4	$ 5,917.7
Financial Services [Member]
Debt Instrument [Line Items]
Notes payable	1,447.4	1,533.8
Commitments to Extend Credit \| Financial Services [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,600.0
Line of Credit Facility, Expiration Date	May 09, 2025
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,000.0
Notes payable	$ 1,364.9	1,229.3
Assets Sold under Agreements to Repurchase, Interest Rate	6.00%
Deposit Liabilities, Collateral Issued, Financial Instruments	$ 2,350.0
Participating Mortgage Loans, Mortgage Obligations, Amount	2,310.0
Warehouse Agreement Borrowings \| Financial Services [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	500.0
Notes payable	$ 82.5	$ 304.5
Assets Sold under Agreements to Repurchase, Interest Rate	5.60%
Deposit Liabilities, Collateral Issued, Financial Instruments	$ 90.5
Participating Mortgage Loans, Mortgage Obligations, Amount	$ 85.8

Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

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