CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 149,746	$ 156,662
Loans and leases, nonaccrual	1,296	944
Loans and leases, nonaccrual with no related ACL	428	456
Current
Financing Receivable, Past Due [Line Items]
Loans and leases	147,433	154,527
30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	533	598
60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	236	226
90+
Financing Receivable, Past Due [Line Items]
Loans and leases	248	367
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	77,457	82,180
Loans and leases, nonaccrual	715	352
Loans and leases, nonaccrual with no related ACL	91	71
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	46,753	51,836
Loans and leases, nonaccrual	242	249
Loans and leases, nonaccrual with no related ACL	43	64
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	29,486	28,865
Loans and leases, nonaccrual	470	103
Loans and leases, nonaccrual with no related ACL	48	7
Commercial | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,218	1,479
Loans and leases, nonaccrual	3	0
Loans and leases, nonaccrual with no related ACL	0	0
Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	76,586	81,529
Commercial | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	46,475	51,389
Commercial | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,896	28,665
Commercial | Current | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,215	1,475
Commercial | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	98	207
Commercial | 30-59 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	23	152
Commercial | 30-59 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	75	51
Commercial | 30-59 | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	4
Commercial | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	51	70
Commercial | 60-89 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	9	25
Commercial | 60-89 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	42	45
Commercial | 60-89 | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Commercial | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	7	22
Commercial | 90+ | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	4	21
Commercial | 90+ | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	3	1
Commercial | 90+ | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail
Financing Receivable, Past Due [Line Items]
Loans and leases	72,289	74,482
Loans and leases, nonaccrual	581	592
Loans and leases, nonaccrual with no related ACL	337	385
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	30,983	29,921
Loans and leases, nonaccrual	190	234
Loans and leases, nonaccrual with no related ACL	149	187
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	14,729	14,043
Loans and leases, nonaccrual	268	241
Loans and leases, nonaccrual with no related ACL	179	185
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	9,290	12,292
Loans and leases, nonaccrual	62	56
Loans and leases, nonaccrual with no related ACL	7	9
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	12,134	12,808
Loans and leases, nonaccrual	23	33
Loans and leases, nonaccrual with no related ACL	2	3
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,153	5,418
Loans and leases, nonaccrual	38	28
Loans and leases, nonaccrual with no related ACL	0	1
Retail | FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases, 90 days or more past due and still accruing	216	316
Retail | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	70,847	72,998
Retail | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	30,416	29,228
Retail | Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	14,351	13,719
Retail | Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	9,031	12,039
Retail | Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	12,035	12,718
Retail | Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,014	5,294
Retail | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	435	391
Retail | 30-59 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	110	95
Retail | 30-59 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	82	64
Retail | 30-59 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	147	152
Retail | 30-59 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	47	36
Retail | 30-59 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	49	44
Retail | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	185	156
Retail | 60-89 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	50	45
Retail | 60-89 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	28	19
Retail | 60-89 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	50	45
Retail | 60-89 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	26	17
Retail | 60-89 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	31	30
Retail | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	241	345
Retail | 90+ | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	217	319
Retail | 90+ | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | 90+ | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | 90+ | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	3	4
Retail | 90+ | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 21	$ 22