Notes Payable - Financial Services Textuals (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Notes payable	$ 7,248.7	$ 5,917.7
Financial Services [Member]
Debt Instrument [Line Items]
Notes payable	1,704.2	1,533.8
Commitments to Extend Credit | Financial Services [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,400.0
Line of Credit Facility, Expiration Date	May 06, 2026
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,000.0
Notes payable	$ 1,252.5	1,229.3
Assets Sold under Agreements to Repurchase, Interest Rate	6.00%
Deposit Liabilities, Collateral Issued, Financial Instruments	$ 2,220.0
Participating Mortgage Loans, Mortgage Obligations, Amount	2,170.0
Warehouse Agreement Borrowings | Financial Services [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	500.0
Notes payable	$ 451.7	$ 304.5
Assets Sold under Agreements to Repurchase, Interest Rate	5.60%
Deposit Liabilities, Collateral Issued, Financial Instruments	$ 535.9
Participating Mortgage Loans, Mortgage Obligations, Amount	$ 501.1