CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Modified (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 1,799	$ 1,595	$ 1,093
Total as a % of Loan Class	1.26%	1.15%	0.75%
Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 1,334	$ 933	$ 724
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	25	110	20
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	14	8	8
Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	28	26	43
Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	398	518	298
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 1,629	$ 1,384	$ 918
Total as a % of Loan Class	2.21%	1.98%	1.23%
Commercial | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 1,262	$ 836	$ 613
Commercial | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	11	95	7
Commercial | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	7	0	0
Commercial | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2	4	26
Commercial | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	347	449	272
Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 342	$ 357	$ 325
Total as a % of Loan Class	0.69%	0.84%	0.74%
Weighted-Average Interest Rate Reduction	1.65%	3.78%	2.02%
Weighted-Average Term Extension (in Months)	18 months	15 months	15 months
Weighted-Average Payment Deferral	$ 0	$ 4	$ 1
Commercial | Commercial and industrial | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	309	290	211
Commercial | Commercial and industrial | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	3	0
Commercial | Commercial and industrial | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2	0	0
Commercial | Commercial and industrial | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Commercial | Commercial and industrial | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	31	64	114
Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 1,287	$ 1,027	$ 593
Total as a % of Loan Class	5.24%	3.77%	2.01%
Weighted-Average Interest Rate Reduction	1.00%	2.83%	0.59%
Weighted-Average Term Extension (in Months)	14 months	17 months	11 months
Weighted-Average Payment Deferral	$ 3	$ 1	$ 0
Commercial | Commercial real estate | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	953	546	402
Commercial | Commercial real estate | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	11	92	7
Commercial | Commercial real estate | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	5	0	0
Commercial | Commercial real estate | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2	4	26
Commercial | Commercial real estate | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	316	385	158
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 170	$ 211	$ 175
Total as a % of Loan Class	0.25%	0.30%	0.24%
Retail | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 72	$ 97	$ 111
Retail | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	14	15	13
Retail | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	7	8	8
Retail | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	26	22	17
Retail | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	51	69	26
Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 108	$ 114	$ 109
Total as a % of Loan Class	0.31%	0.35%	0.35%
Weighted-Average Interest Rate Reduction	1.04%	1.83%	1.58%
Weighted-Average Term Extension (in Months)	111 months	94 months	50 months
Weighted-Average Payment Deferral	$ 0	$ 0	$ 0
Retail | Residential mortgages | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	43	49	61
Retail | Residential mortgages | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	12	13	11
Retail | Residential mortgages | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	6	7	7
Retail | Residential mortgages | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	26	22	17
Retail | Residential mortgages | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	21	23	13
Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 33	$ 23	$ 15
Total as a % of Loan Class	0.17%	0.14%	0.10%
Weighted-Average Interest Rate Reduction	3.19%	4.01%	2.64%
Weighted-Average Term Extension (in Months)	144 months	71 months	120 months
Weighted-Average Payment Deferral	$ 0	$ 0	$ 0
Retail | Home equity | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	6	10	5
Retail | Home equity | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Retail | Home equity | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Retail | Home equity | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Retail | Home equity | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	27	13	$ 10
Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Weighted-Average Interest Rate Reduction			3.60%
Weighted-Average Term Extension (in Months)			18 months
Weighted-Average Payment Deferral			$ 0
Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 11	$ 58	$ 40
Total as a % of Loan Class	0.13%	0.54%	0.34%
Weighted-Average Interest Rate Reduction	4.83%	4.41%	4.76%
Weighted-Average Term Extension (in Months)		12 months
Weighted-Average Payment Deferral	$ 0	$ 0	$ 0
Retail | Education | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	9	26	37
Retail | Education | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	1
Retail | Education | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Retail | Education | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Retail | Education | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2	32	2
Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 18	$ 16	$ 11
Total as a % of Loan Class	0.44%	0.34%	0.22%
Weighted-Average Interest Rate Reduction	19.90%	20.18%	18.68%
Weighted-Average Payment Deferral	$ 0	$ 0	$ 0
Retail | Other retail | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	14	12	8
Retail | Other retail | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2	2	1
Retail | Other retail | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1	1	1
Retail | Other retail | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Retail | Other retail | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1	1	1
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	87	39	31
Interest Rate Reduction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	47	0	1
Interest Rate Reduction | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	16	0	1
Interest Rate Reduction | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	31	0	0
Interest Rate Reduction | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	40	39	30
Interest Rate Reduction | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3	6	8
Interest Rate Reduction | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	8	6	2
Interest Rate Reduction | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	11	11	9
Interest Rate Reduction | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	18	16	11
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,316	965	856
Term Extension | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,246	885	774
Term Extension | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	314	235	252
Term Extension | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	932	650	522
Term Extension | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	70	80	82
Term Extension | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	67	74	77
Term Extension | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3	3	5
Term Extension | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	3	0
Term Extension | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Payment Delay
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	127	259	103
Payment Delay | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	97	212	69
Payment Delay | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2	99	69
Payment Delay | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	95	113	0
Payment Delay | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	30	47	34
Payment Delay | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	17	12	3
Payment Delay | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	13	1	0
Payment Delay | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	34	31
Payment Delay | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Principal Forgiveness | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven	0	0	0
Principal Forgiveness | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven	0	0	0
Principal Forgiveness | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven	0	0	0
Principal Forgiveness | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven	0	0	0
Principal Forgiveness | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven			0
Principal Forgiveness | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven	0	0	0
Principal Forgiveness | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amount of Principal Forgiven	16	6	5
Interest Rate Reduction and Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	72	160	99
Interest Rate Reduction and Term Extension | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	48	131	71
Interest Rate Reduction and Term Extension | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	5	1	1
Interest Rate Reduction and Term Extension | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	43	130	70
Interest Rate Reduction and Term Extension | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	24	29	28
Interest Rate Reduction and Term Extension | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	15	16	20
Interest Rate Reduction and Term Extension | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	9	13	8
Interest Rate Reduction and Term Extension | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Interest Rate Reduction and Term Extension | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Term Extension and Payment Delay
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	165	170	4
Term Extension and Payment Delay | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	162	155	3
Term Extension and Payment Delay | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1	21	2
Term Extension and Payment Delay | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	161	134	1
Term Extension and Payment Delay | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3	15	1
Term Extension and Payment Delay | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3	5	1
Term Extension and Payment Delay | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	0
Term Extension and Payment Delay | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	10	0
Term Extension and Payment Delay | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0	$ 0
Interest Rate Reduction, Term Extension, and Payment Delay
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	32	2
Interest Rate Reduction, Term Extension, and Payment Delay | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	29	1
Interest Rate Reduction, Term Extension, and Payment Delay | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	4	1
Interest Rate Reduction, Term Extension, and Payment Delay | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	25	0
Interest Rate Reduction, Term Extension, and Payment Delay | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3	1
Interest Rate Reduction, Term Extension, and Payment Delay | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3	1
Interest Rate Reduction, Term Extension, and Payment Delay | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction, Term Extension, and Payment Delay | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction, Term Extension, and Payment Delay | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 0	$ 0