COMMITMENTS, CONTINGENCIES AND GUARANTEES, Summary of Commitments to Extend Credit and Other Credit-Related Off-Balance Sheet Financial Instruments Outstanding (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Open-end consumer lines of credit (primarily SBL)	$ 10,758	$ 9,328
Commercial lines of credit	1,153	1,527
Unfunded loan commitments	676	599
Standby letters of credit	$ 40	$ 40