CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 137,635	$ 139,203
Loans and leases, nonaccrual	1,582	1,664
Loans and leases, nonaccrual with no related ACL	398	398
Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	1,012	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	135,245	136,320
Current | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	824	696
30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	502	769
30-59 | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	32	119
60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	151	254
60-89 | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	19	55
90+
Financing Receivable, Past Due [Line Items]
Loans and leases	155	196
90+ | Guaranteed residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	137	172
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	70,508	69,776
Loans and leases, nonaccrual	983	1,017
Loans and leases, nonaccrual with no related ACL	64	63
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	43,781	42,551
Loans and leases, nonaccrual	283	241
Loans and leases, nonaccrual with no related ACL	45	31
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	26,727	27,225
Loans and leases, nonaccrual	700	776
Loans and leases, nonaccrual with no related ACL	19	32
Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	69,307	68,459
Commercial | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	43,420	42,247
Commercial | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	25,887	26,212
Commercial | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	187	239
Commercial | 30-59 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	56	35
Commercial | 30-59 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	131	204
Commercial | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	18	47
Commercial | 60-89 | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	13	20
Commercial | 60-89 | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	5	27
Commercial | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	13	14
Commercial | 90+ | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	9	8
Commercial | 90+ | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	4	6
Retail
Financing Receivable, Past Due [Line Items]
Loans and leases	67,127	69,427
Loans and leases, nonaccrual	599	647
Loans and leases, nonaccrual with no related ACL	334	335
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	33,114	32,726
Loans and leases, nonaccrual	198	192
Loans and leases, nonaccrual with no related ACL	147	142
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	16,853	16,495
Loans and leases, nonaccrual	282	283
Loans and leases, nonaccrual with no related ACL	178	182
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	4,044	4,744
Loans and leases, nonaccrual	39	48
Loans and leases, nonaccrual with no related ACL	6	6
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	8,779	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	4,337	4,650
Loans and leases, nonaccrual	60	68
Loans and leases, nonaccrual with no related ACL	1	1
Retail | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	65,938	67,861
Retail | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	32,682	32,011
Retail | Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	16,450	16,097
Retail | Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	3,900	4,563
Retail | Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	8,699	10,686
Retail | Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	4,207	4,504
Retail | 30-59
Financing Receivable, Past Due [Line Items]
Loans and leases	315	530
Retail | 30-59 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	60	251
Retail | 30-59 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	94	88
Retail | 30-59 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	80	100
Retail | 30-59 | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	39	45
Retail | 30-59 | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	42	46
Retail | 60-89
Financing Receivable, Past Due [Line Items]
Loans and leases	133	207
Retail | 60-89 | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	36	93
Retail | 60-89 | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	27	27
Retail | 60-89 | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	25	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	27	31
Retail | 90+
Financing Receivable, Past Due [Line Items]
Loans and leases	142	182
Retail | 90+ | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	138	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	3	2
Retail | 90+ | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 1	$ 1