CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 140,870	$ 139,203
Loans and leases, nonaccrual	1,518	1,664
Loans and leases, nonaccrual with no related ACL	412	398
Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	976	1,042
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	138,545	136,320
Current | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	795	696
30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	433	769
30-59 | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	44	119
60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	212	254
60-89 | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	23	55
90+
Financing Receivable, Past Due [Line Items]
Loans and leases	162	196
90+ | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	114	172
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	72,493	69,776
Loans and leases, nonaccrual	933	1,017
Loans and leases, nonaccrual with no related ACL	49	63
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	46,953	42,551
Loans and leases, nonaccrual	230	241
Loans and leases, nonaccrual with no related ACL	24	31
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	25,540	27,225
Loans and leases, nonaccrual	703	776
Loans and leases, nonaccrual with no related ACL	25	32
Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	71,292	68,459
Commercial | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	46,624	42,247
Commercial | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	24,668	26,212
Commercial | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	142	239
Commercial | 30-59 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	52	35
Commercial | 30-59 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	90	204
Commercial | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	80	47
Commercial | 60-89 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	8	20
Commercial | 60-89 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	72	27
Commercial | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	46	14
Commercial | 90+ | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	39	8
Commercial | 90+ | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	7	6
Retail
Financing Receivable, Past Due [Line Items]
Loans and leases	68,377	69,427
Loans and leases, nonaccrual	585	647
Loans and leases, nonaccrual with no related ACL	363	335
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	34,477	32,726
Loans and leases, nonaccrual	188	192
Loans and leases, nonaccrual with no related ACL	150	142
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	18,415	16,495
Loans and leases, nonaccrual	297	283
Loans and leases, nonaccrual with no related ACL	206	182
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	2,816	4,744
Loans and leases, nonaccrual	31	48
Loans and leases, nonaccrual with no related ACL	4	6
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	8,556	10,812
Loans and leases, nonaccrual	20	56
Loans and leases, nonaccrual with no related ACL	2	4
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	4,113	4,650
Loans and leases, nonaccrual	49	68
Loans and leases, nonaccrual with no related ACL	1	1
Retail | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	67,253	67,861
Retail | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	34,052	32,011
Retail | Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	18,007	16,097
Retail | Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	2,702	4,563
Retail | Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	8,482	10,686
Retail | Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	4,010	4,504
Retail | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	291	530
Retail | 30-59 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	80	251
Retail | 30-59 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	83	88
Retail | 30-59 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	62	100
Retail | 30-59 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	34	45
Retail | 30-59 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	32	46
Retail | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	132	207
Retail | 60-89 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	43	93
Retail | 60-89 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	28	27
Retail | 60-89 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	21	33
Retail | 60-89 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	18	23
Retail | 60-89 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	22	31
Retail | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	116	182
Retail | 90+ | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	114	179
Retail | 90+ | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
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	$ 1