v3.26.1
COLLATERALIZED AGREEMENTS AND FINANCINGS, Encumbered Assets (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Asset pledged as collateral | Assets pledged at the FHLB or FRB:    
Financial Instruments Owned and Pledged as Collateral [Line Items]    
Financial instruments, owned, at fair value $ 35,818 $ 33,449
Asset pledged as collateral | Assets pledged at the FHLB or FRB: | Available-for-sale securities    
Financial Instruments Owned and Pledged as Collateral [Line Items]    
Financial instruments, owned, at fair value 2,216 2,435
Asset pledged as collateral | Assets pledged at the FHLB or FRB: | Bank loans    
Financial Instruments Owned and Pledged as Collateral [Line Items]    
Financial instruments, owned, at fair value 33,602 31,014
Had the right to deliver or repledge    
Financial Instruments Owned and Pledged as Collateral [Line Items]    
Financial instruments, owned, at fair value 1,381 1,265
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 $ 66