CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructuring Activity (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2022 USD ($) contract	Jun. 30, 2022 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,178	3,376
Amortized Cost Basis	$ 119	$ 421
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	19	46
Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	40	78
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 60	$ 297
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	9	19
Amortized Cost Basis	$ 27	$ 58
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	0	24
Commercial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 27	$ 34
Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	9	19
Amortized Cost Basis	$ 27	$ 58
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	0	24
Commercial | Commercial and industrial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 27	$ 34
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,169	3,357
Amortized Cost Basis	$ 92	$ 363
Retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	19	46
Retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	40	54
Retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 33	$ 263
Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	290	1,471
Amortized Cost Basis	$ 76	$ 326
Retail | Residential mortgages | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	16	38
Retail | Residential mortgages | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	39	53
Retail | Residential mortgages | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 21	$ 235
Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	72	250
Amortized Cost Basis	$ 6	$ 17
Retail | Home equity | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	0	2
Retail | Home equity | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	1	1
Retail | Home equity | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	$ 5	$ 14
Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	147	312
Amortized Cost Basis	$ 1	$ 3
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	$ 2
Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	93	236
Amortized Cost Basis	$ 5	$ 11
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	$ 5	$ 11
Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	567	1,088
Amortized Cost Basis	$ 4	$ 6
Retail | Other retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost Basis	3	5
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	$ 1	$ 1