COLLATERALIZED AGREEMENTS AND FINANCINGS, Encumbered Assets (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Asset pledged as collateral | Assets pledged with the FHLB or FRB:
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	$ 15,773	$ 14,063
Asset pledged as collateral | Assets pledged with the FHLB or FRB: | Debt Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	3,979	3,897
Asset pledged as collateral | Assets pledged with the FHLB or FRB: | Loans Receivable
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	11,794	10,166
Had the right to deliver or repledge
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	1,281	1,091
Did not have the right to deliver or repledge
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments, owned, at fair value	$ 66	$ 63