ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 154,688	$ 156,662
Loans and leases, nonaccrual	996	944
Loans and leases, nonaccrual with no related ACL	418	456
Current
Financing Receivable, Past Due [Line Items]
Loans and leases	152,259	154,527
30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	824	598
60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	185	226
90+
Financing Receivable, Past Due [Line Items]
Loans and leases	424	367
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	80,866	82,180
Loans and leases, nonaccrual	437	352
Loans and leases, nonaccrual with no related ACL	64	71
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	50,450	51,836
Loans and leases, nonaccrual	297	249
Loans and leases, nonaccrual with no related ACL	63	64
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,999	28,865
Loans and leases, nonaccrual	140	103
Loans and leases, nonaccrual with no related ACL	1	7
Commercial | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,417	1,479
Loans and leases, nonaccrual	0	0
Loans and leases, nonaccrual with no related ACL	0	0
Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	79,981	81,529
Commercial | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	50,007	51,389
Commercial | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,558	28,665
Commercial | Current | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,416	1,475
Commercial | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	351	207
Commercial | 30-59 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	119	152
Commercial | 30-59 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	231	51
Commercial | 30-59 | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1	4
Commercial | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	13	70
Commercial | 60-89 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	6	25
Commercial | 60-89 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	7	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	84	22
Commercial | 90+ | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	21	21
Commercial | 90+ | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	63	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	73,822	74,482
Loans and leases, nonaccrual	559	592
Loans and leases, nonaccrual with no related ACL	354	385
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	30,362	29,921
Loans and leases, nonaccrual	216	234
Loans and leases, nonaccrual with no related ACL	162	187
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	14,135	14,043
Loans and leases, nonaccrual	240	241
Loans and leases, nonaccrual with no related ACL	180	185
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	11,535	12,292
Loans and leases, nonaccrual	50	56
Loans and leases, nonaccrual with no related ACL	8	9
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	12,634	12,808
Loans and leases, nonaccrual	23	33
Loans and leases, nonaccrual with no related ACL	3	3
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,156	5,418
Loans and leases, nonaccrual	30	28
Loans and leases, nonaccrual with no related ACL	1	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	309	316
Retail | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	72,278	72,998
Retail | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	29,556	29,228
Retail | Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	13,804	13,719
Retail | Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	11,323	12,039
Retail | Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	12,561	12,718
Retail | Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,034	5,294
Retail | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	473	391
Retail | 30-59 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	202	95
Retail | 30-59 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	68	64
Retail | 30-59 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	128	152
Retail | 30-59 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	33	36
Retail | 30-59 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	42	44
Retail | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	172	156
Retail | 60-89 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	74	45
Retail | 60-89 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	23	19
Retail | 60-89 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	34	45
Retail | 60-89 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	14	17
Retail | 60-89 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	27	30
Retail | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	340	345
Retail | 90+ | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	314	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	$ 23	$ 22