CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructuring Activity (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022 USD ($) contract	Sep. 30, 2022 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,229	4,605
Amortized Cost Basis	$ 103	$ 524
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	10	56
Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	23	101
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 70	$ 367
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	6	25
Amortized Cost Basis	$ 48	$ 106
Commercial | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0
Commercial | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	26
Commercial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 46	$ 80
Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	6	25
Amortized Cost Basis	$ 48	$ 106
Commercial | Commercial and industrial | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0
Commercial | Commercial and industrial | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	26
Commercial | Commercial and industrial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 46	$ 80
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,223	4,580
Amortized Cost Basis	$ 55	$ 418
Retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	10	56
Retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	21	75
Retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 24	$ 287
Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	185	1,656
Amortized Cost Basis	$ 40	$ 366
Retail | Residential mortgages | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	6	44
Retail | Residential mortgages | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	21	74
Retail | Residential mortgages | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 13	$ 248
Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	68	318
Amortized Cost Basis	$ 4	$ 21
Retail | Home equity | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	4
Retail | Home equity | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	1
Retail | Home equity | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 2	$ 16
Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	135	447
Amortized Cost Basis	$ 1	$ 4
Retail | Automobile | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	1
Retail | Automobile | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0
Retail | Automobile | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 1	$ 3
Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	245	481
Amortized Cost Basis	$ 8	$ 19
Retail | Education | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0
Retail | Education | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0
Retail | Education | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 8	$ 19
Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	590	1,678
Amortized Cost Basis	$ 2	$ 8
Retail | Other retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	2	7
Retail | Other retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	0
Retail | Other retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 0	$ 1