ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring Activity (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) contract	Sep. 30, 2021 USD ($) contract	Sep. 30, 2022 USD ($) contract	Sep. 30, 2021 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,229	1,176	4,605	4,835
Amortized Cost Basis	$ 103	$ 81	$ 524	$ 376
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	10	5	56	25
Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	23	46	101	186
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 70	$ 30	$ 367	$ 165
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	6	7	25	29
Amortized Cost Basis	$ 48	$ 48	$ 106	$ 108
Commercial | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	0	0
Commercial | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	38	26	44
Commercial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 46	$ 10	$ 80	$ 64
Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	6	7	25	29
Amortized Cost Basis	$ 48	$ 48	$ 106	$ 108
Commercial | Commercial and industrial | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	0	0
Commercial | Commercial and industrial | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	38	26	44
Commercial | Commercial and industrial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 46	$ 10	$ 80	$ 64
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,223	1,169	4,580	4,806
Amortized Cost Basis	$ 55	$ 33	$ 418	$ 268
Retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	10	5	56	25
Retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	21	8	75	142
Retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 24	$ 20	$ 287	$ 101
Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	185	101	1,656	814
Amortized Cost Basis	$ 40	$ 16	$ 366	$ 201
Retail | Residential mortgages | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	6	2	44	14
Retail | Residential mortgages | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	21	7	74	133
Retail | Residential mortgages | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 13	$ 7	$ 248	$ 54
Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	68	69	318	318
Amortized Cost Basis	$ 4	$ 4	$ 21	$ 22
Retail | Home equity | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	0	4	3
Retail | Home equity | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	1	1	9
Retail | Home equity | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 2	$ 3	$ 16	$ 10
Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	135	224	447	1,272
Amortized Cost Basis	$ 1	$ 1	$ 4	$ 15
Retail | Automobile | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	1	1
Retail | Automobile | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	0	0
Retail | Automobile | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 1	$ 1	$ 3	$ 14
Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	245	226	481	638
Amortized Cost Basis	$ 8	$ 8	$ 19	$ 21
Retail | Education | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	0	0
Retail | Education | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	0	0
Retail | Education | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 8	$ 8	$ 19	$ 21
Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	590	549	1,678	1,764
Amortized Cost Basis	$ 2	$ 4	$ 8	$ 9
Retail | Other retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	3	7	7
Retail | Other retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0	0	0
Retail | Other retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 0	$ 1	$ 1	$ 2