SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) component institution subsidiary investor risk_factor tax_credit_fund segment	Sep. 30, 2019 USD ($)
Bank loans and allowances for losses [Abstract]
Number of loan portfolio segments | segment	6
Minimum past due for loans placed on nonaccrual status (or more)	90 days
Period of satisfactory performance for loans to be returned to accrual status (in months)	6 months
Number of components comprising the allowance for loan loss | component	2
Number of aspects of risk factors analyzed | risk_factor	2
Minimum amount of Shared National Credit (SNC) loan syndications | $	$ 100
Minimum number of regulated institutions with which SNCs are shared (or more) | institution	3
Minimum past due for residential loans to be reviewed (in days)	60 days
Minimum past due for charge-offs to be considered on residential mortgage loans (in days)	90 days
Maximum past due for charge-offs taken on residential mortgage loans (in days)	120 days
Minimum period for which updated valuation is obtained for loans in pre-foreclosure status (in months)	9 months
Brokerage client receivables and loans to financial advisors [Abstract]
Repayment period of loans to financial advisors and certain key revenue producers, minimum (in years)	5 years
Repayment period of loans to financial advisors and certain key revenue producers, maximum (in years)	9 years
Loans associated with financial advisors no longer affiliated with the entity, allowance | $	$ 4	$ 9
LIHTC Funds [Abstract]
Minimum number of investor members or limited partners of LIHTC Funds (or more) | investor	1
Number of general types of non-guaranteed tax credit funds | tax_credit_fund	2
Number of single investor members or limited partners in funds | subsidiary	1
Number of party with power | subsidiary	1