COMMITMENTS, CONTINGENCIES AND GUARANTEES, Summary of Commitments to Extend Credit and Other Credit-Related Off-Balance Sheet Financial Instruments Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Open-end consumer lines of credit (primarily SBL)	$ 13,120	$ 12,148
Commercial lines of credit	1,560	1,482
Unfunded loan commitments	566	532
Standby letters of credit	$ 31	$ 33