SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Other Narrative (Details) $ in Millions		12 Months Ended
	Jun. 01, 2022	Sep. 30, 2024 USD ($) tax_credit_fund investor institution portfolio_segment	Sep. 30, 2023	Sep. 30, 2022
Bank loans and allowances for losses [Abstract]
Loan discounts, fair value adjustments, amortization period	4 years
Number of loan portfolio segments | portfolio_segment		6
Letters of credit, expiration period		1 year
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		6 months
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		60 days
Minimum past due for charge-offs to be considered on residential mortgage loans		90 days
Maximum past due for charge-offs taken on residential mortgage loans		120 days
Minimum period for which updated valuation is obtained for loans in pre-foreclosure status		9 months
Brokerage client receivables and loans to financial advisors [Abstract]
Repayment period of loans to financial advisors and certain key revenue producers, minimum		5 years
Repayment period of loans to financial advisors and certain key revenue producers, maximum		10 years
Income taxes
Amortization of investments accounted for under the proportional amortization method, statements of cash flows location		Net Cash Provided by (Used in) Operating Activities	Net Cash Provided by (Used in) Operating Activities	Net Cash Provided by (Used in) Operating Activities
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 | investor		1
Number of party with power | tax_credit_fund		1