ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring Activity (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) contract	Dec. 31, 2021 USD ($) contract	Dec. 31, 2020 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	5,846	5,939	7,559
Amortized Cost	$ 501	$ 468	$ 644
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	68	37	63
Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	124	192	161
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 309	$ 239	$ 420
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	29	44	71
Amortized Cost	$ 26	$ 167	$ 439
Commercial | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	0	0	0
Commercial | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	26	44	114
Commercial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0	$ 123	$ 325
Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	29	44	70
Amortized Cost	$ 26	$ 167	$ 432
Commercial | Commercial and industrial | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	0	0	0
Commercial | Commercial and industrial | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	26	44	107
Commercial | Commercial and industrial | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 0	$ 123	$ 325
Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract			1
Amortized Cost			$ 7
Commercial | Commercial real estate | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			0
Commercial | Commercial real estate | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			7
Commercial | Commercial real estate | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost			$ 0
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	5,817	5,895	7,488
Amortized Cost	$ 475	$ 301	$ 205
Retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	68	37	63
Retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	98	148	47
Retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 309	$ 116	$ 95
Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	1,884	922	473
Amortized Cost	$ 408	$ 218	$ 86
Retail | Residential mortgages | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	52	21	39
Retail | Residential mortgages | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	96	137	34
Retail | Residential mortgages | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 260	$ 60	$ 13
Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	381	412	723
Amortized Cost	$ 25	$ 29	$ 47
Retail | Home equity | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	4	5	12
Retail | Home equity | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	2	11	12
Retail | Home equity | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 19	$ 13	$ 23
Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	601	1,463	3,236
Amortized Cost	$ 6	$ 17	$ 50
Retail | Automobile | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	2	2	2
Retail | Automobile | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	0	0	1
Retail | Automobile | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 4	$ 15	$ 47
Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	631	807	465
Amortized Cost	$ 25	$ 26	$ 10
Retail | Education | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	0	0	0
Retail | Education | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	0	0	0
Retail | Education | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 25	$ 26	$ 10
Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | contract	2,320	2,291	2,591
Amortized Cost	$ 11	$ 11	$ 12
Retail | Other retail | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	10	9	10
Retail | Other retail | Maturity Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	0	0	0
Retail | Other retail | Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized Cost	$ 1	$ 2	$ 2