LOANS, LEASES, AND ALLOWANCE FOR CREDIT LOSSES (Summary Aging Analysis, Modified) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 307	$ 243
Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	285	227
Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	22	16
30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	12	16
90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	10	0
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	100	76
Commercial | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	85	73
Commercial | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	15	3
Commercial | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	12	3
Commercial | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	3	0
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	83	64
Commercial | Commercial and industrial | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	76	64
Commercial | Commercial and industrial | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	7	0
Commercial | Commercial and industrial | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4	0
Commercial | Commercial and industrial | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	3	0
Commercial | Owner-occupied
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	6	12
Commercial | Owner-occupied | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	6	9
Commercial | Owner-occupied | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	3
Commercial | Owner-occupied | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	3
Commercial | Owner-occupied | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Commercial | Municipal
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	11
Commercial | Municipal | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	3
Commercial | Municipal | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	8
Commercial | Municipal | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	8
Commercial | Municipal | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	201	164
Commercial real estate | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	194	151
Commercial real estate | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	7	13
Commercial real estate | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	13
Commercial real estate | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	7	0
Commercial real estate | Construction and land development
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	26	23
Commercial real estate | Construction and land development | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	24	23
Commercial real estate | Construction and land development | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2	0
Commercial real estate | Construction and land development | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Commercial real estate | Construction and land development | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	2	0
Commercial real estate | Term
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	175	141
Commercial real estate | Term | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	170	128
Commercial real estate | Term | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	5	13
Commercial real estate | Term | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	13
Commercial real estate | Term | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	5	0
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	6	3
Consumer | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	6	3
Consumer | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Consumer | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Consumer | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Consumer | Home equity credit line
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1
Consumer | Home equity credit line | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1
Consumer | Home equity credit line | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0
Consumer | Home equity credit line | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0
Consumer | Home equity credit line | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0
Consumer | 1-4 family residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4	2
Consumer | 1-4 family residential | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	4	2
Consumer | 1-4 family residential | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Consumer | 1-4 family residential | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Consumer | 1-4 family residential | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0	0
Consumer | Bankcard and other revolving plans
Financing Receivable, Allowance for Credit Losses [Line Items]
Total		1
Consumer | Bankcard and other revolving plans | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total		1
Consumer | Bankcard and other revolving plans | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total		0
Consumer | Bankcard and other revolving plans | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total		0
Consumer | Bankcard and other revolving plans | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total		$ 0
Consumer | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1
Consumer | Other | Current
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	1
Consumer | Other | Total past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0
Consumer | Other | 30-89 days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	0
Consumer | Other | 90+ days past due
Financing Receivable, Allowance for Credit Losses [Line Items]
Total	$ 0