CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Accruing and Non-accruing Past Due Amounts (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 145,959	$ 156,662
Loans and leases, nonaccrual	1,364	944
Loans and leases, nonaccrual with no related ACL	453	456
FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases	1,122	1,196
Loans and leases, nonaccrual	0	0
Loans and leases, nonaccrual with no related ACL	0	0
Financing Receivables, Current
Financing Receivable, Past Due [Line Items]
Loans and leases	143,111	154,527
Financing Receivables, Current | FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases	675	789
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	818	598
Financing Receivables, 30 to 59 Days Past Due | FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases	128	57
Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	333	226
Financing Receivables, 60 to 89 Days Past Due | FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases	76	34
Financing Receivables, 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	333	367
Financing Receivables, 90 Days or More Past Due | FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases	243	316
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	74,445	82,180
Loans and leases, nonaccrual	774	352
Loans and leases, nonaccrual with no related ACL	101	71
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	43,826	51,836
Loans and leases, nonaccrual	294	249
Loans and leases, nonaccrual with no related ACL	30	64
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	29,471	28,865
Loans and leases, nonaccrual	477	103
Loans and leases, nonaccrual with no related ACL	71	7
Commercial | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,148	1,479
Loans and leases, nonaccrual	3	0
Loans and leases, nonaccrual with no related ACL	0	0
Commercial | Financing Receivables, Current
Financing Receivable, Past Due [Line Items]
Loans and leases	73,336	81,529
Commercial | Financing Receivables, Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	43,447	51,389
Commercial | Financing Receivables, Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,745	28,665
Commercial | Financing Receivables, Current | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,144	1,475
Commercial | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	212	207
Commercial | Financing Receivables, 30 to 59 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	61	152
Commercial | Financing Receivables, 30 to 59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	150	51
Commercial | Financing Receivables, 30 to 59 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1	4
Commercial | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	77	70
Commercial | Financing Receivables, 60 to 89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	18	25
Commercial | Financing Receivables, 60 to 89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	59	45
Commercial | Financing Receivables, 60 to 89 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Commercial | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	46	22
Commercial | Financing Receivables, 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	6	21
Commercial | Financing Receivables, 90 Days or More Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	40	1
Commercial | Financing Receivables, 90 Days or More Past Due | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail
Financing Receivable, Past Due [Line Items]
Loans and leases	71,514	74,482
Loans and leases, nonaccrual	590	592
Loans and leases, nonaccrual with no related ACL	352	385
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	31,332	29,921
Loans and leases, nonaccrual	177	234
Loans and leases, nonaccrual with no related ACL	144	187
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	15,040	14,043
Loans and leases, nonaccrual	285	241
Loans and leases, nonaccrual with no related ACL	198	185
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	8,258	12,292
Loans and leases, nonaccrual	61	56
Loans and leases, nonaccrual with no related ACL	7	9
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	11,834	12,808
Loans and leases, nonaccrual	28	33
Loans and leases, nonaccrual with no related ACL	3	3
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,050	5,418
Loans and leases, nonaccrual	39	28
Loans and leases, nonaccrual with no related ACL	0	1
Retail | Financing Receivables, Current
Financing Receivable, Past Due [Line Items]
Loans and leases	69,775	72,998
Retail | Financing Receivables, Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	30,499	29,228
Retail | Financing Receivables, Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	14,640	13,719
Retail | Financing Receivables, Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	8,005	12,039
Retail | Financing Receivables, Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	11,732	12,718
Retail | Financing Receivables, Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	4,899	5,294
Retail | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	606	391
Retail | Financing Receivables, 30 to 59 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	282	95
Retail | Financing Receivables, 30 to 59 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	82	64
Retail | Financing Receivables, 30 to 59 Days Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	144	152
Retail | Financing Receivables, 30 to 59 Days Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	49	36
Retail | Financing Receivables, 30 to 59 Days Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	49	44
Retail | Financing Receivables, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	256	156
Retail | Financing Receivables, 60 to 89 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	118	45
Retail | Financing Receivables, 60 to 89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	33	19
Retail | Financing Receivables, 60 to 89 Days Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	48	45
Retail | Financing Receivables, 60 to 89 Days Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	23	17
Retail | Financing Receivables, 60 to 89 Days Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	34	30
Retail | Financing Receivables, 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	287	345
Retail | Financing Receivables, 90 Days or More Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	256	319
Retail | Financing Receivables, 90 Days or More Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | Financing Receivables, 90 Days or More Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | Financing Receivables, 90 Days or More Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	2	4
Retail | Financing Receivables, 90 Days or More Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 29	$ 22