DERIVATIVE ASSETS AND DERIVATIVE LIABILITIES, Income Statement Location (Details) - Derivatives not designated as hedging instruments - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Principal transactions/other revenues | Interest rate
Derivative Instruments, Gain (Loss) [Line Items]
Location of gain/(loss)	$ 7	$ 7	$ 6
Other revenues | Foreign exchange
Derivative Instruments, Gain (Loss) [Line Items]
Location of gain/(loss)	0	25	18
Principal transactions | Other
Derivative Instruments, Gain (Loss) [Line Items]
Location of gain/(loss)	(5)	0	0
Compensation, commissions and benefits expense | Other
Derivative Instruments, Gain (Loss) [Line Items]
Location of gain/(loss)	$ (1)	$ 5	$ 8