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Borrowings - Adviser Revolver (Narrative) (Details) - USD ($)	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Sep. 30, 2024	Jun. 11, 2024	Jun. 10, 2024
Debt Instrument [Line Items]
Long-term debt	$ 4,890,564,000		$ 4,599,430,000
Average stated interest rate	6.20%	5.40%
Adviser Revolver \| Line of Credit
Debt Instrument [Line Items]
Long-term debt	$ 0		$ 0
Other Short-Term Borrowings
Debt Instrument [Line Items]
Short-term debt, average outstanding amount	4,770,127,000	$ 3,078,186,000
Revolving Credit Facility \| Adviser Revolver \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 200,000,000			$ 200,000,000	$ 100,000,000
Interest rate	4.20%