CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 143,667	$ 142,692
Loans and leases, nonaccrual	1,497	1,504
Loans and leases, nonaccrual with no related ACL	428	496
Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	951	964
Loans and leases, nonaccrual	0	0
Loans and leases, nonaccrual with no related ACL	0	0
Current
Financing Receivable, Past Due [Line Items]
Loans and leases	140,989	140,248
Current | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	725	743
30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	783	565
30-59 | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	28	53
60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	190	206
60-89 | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	19	27
90+
Financing Receivable, Past Due [Line Items]
Loans and leases	208	169
90+ | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	179	141
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	74,589	73,812
Loans and leases, nonaccrual	867	895
Loans and leases, nonaccrual with no related ACL	74	119
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	50,307	49,232
Loans and leases, nonaccrual	188	277
Loans and leases, nonaccrual with no related ACL	21	34
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	24,282	24,580
Loans and leases, nonaccrual	679	618
Loans and leases, nonaccrual with no related ACL	53	85
Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	73,131	72,573
Commercial | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	49,984	48,873
Commercial | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	23,147	23,700
Commercial | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	495	247
Commercial | 30-59 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	122	63
Commercial | 30-59 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	373	184
Commercial | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	69	72
Commercial | 60-89 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	12	14
Commercial | 60-89 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	57	58
Commercial | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	27	25
Commercial | 90+ | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	1	5
Commercial | 90+ | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	26	20
Retail
Financing Receivable, Past Due [Line Items]
Loans and leases	69,078	68,880
Loans and leases, nonaccrual	630	609
Loans and leases, nonaccrual with no related ACL	354	377
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	35,404	35,024
Loans and leases, nonaccrual	217	196
Loans and leases, nonaccrual with no related ACL	140	155
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	19,449	19,069
Loans and leases, nonaccrual	324	319
Loans and leases, nonaccrual with no related ACL	204	215
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	1,863	2,310
Loans and leases, nonaccrual	23	28
Loans and leases, nonaccrual with no related ACL	3	4
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	8,340	8,416
Loans and leases, nonaccrual	21	20
Loans and leases, nonaccrual with no related ACL	6	2
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	4,022	4,061
Loans and leases, nonaccrual	45	46
Loans and leases, nonaccrual with no related ACL	1	1
Retail | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	67,858	67,675
Retail | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	34,903	34,547
Retail | Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	18,987	18,626
Retail | Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	1,776	2,203
Retail | Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	8,266	8,342
Retail | Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	3,926	3,957
Retail | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	288	318
Retail | 30-59 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	70	93
Retail | 30-59 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	105	95
Retail | 30-59 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	49	59
Retail | 30-59 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	33	36
Retail | 30-59 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	31	35
Retail | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	121	134
Retail | 60-89 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	35	47
Retail | 60-89 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	33	28
Retail | 60-89 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	15	20
Retail | 60-89 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	18	16
Retail | 60-89 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	20	23
Retail | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	181	144
Retail | 90+ | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	179	141
Retail | 90+ | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	0	1
Retail | 90+ | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | 90+ | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	2	2
Retail | 90+ | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 0	$ 0