ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 156,140	$ 128,163
Loans and leases, nonaccrual	852	702
Loans and leases, nonaccrual with no related ACL	457	386
Current
Financing Receivable, Past Due [Line Items]
Loans and leases	154,111	126,308
Financing Receivables, 30 to 59 Days Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	517	412
Financing Receivables 60 To 89 Days Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	198	166
Financing Receivables 90 Days or More Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	462	575
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	81,114	60,350
Loans and leases, nonaccrual	271	183
Loans and leases, nonaccrual with no related ACL	55	37
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	50,989	44,500
Loans and leases, nonaccrual	234	171
Loans and leases, nonaccrual with no related ACL	52	36
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,681	14,264
Loans and leases, nonaccrual	37	11
Loans and leases, nonaccrual with no related ACL	3	1
Commercial | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,444	1,586
Loans and leases, nonaccrual	0	1
Loans and leases, nonaccrual with no related ACL	0	0
Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	80,563	60,064
Commercial | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	50,637	44,247
Commercial | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,483	14,247
Commercial | Current | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,443	1,570
Commercial | Financing Receivables, 30 to 59 Days Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	208	67
Commercial | Financing Receivables, 30 to 59 Days Past Due and Accruing | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	71	47
Commercial | Financing Receivables, 30 to 59 Days Past Due and Accruing | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	136	6
Commercial | Financing Receivables, 30 to 59 Days Past Due and Accruing | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1	14
Commercial | Financing Receivables 60 To 89 Days Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	57	27
Commercial | Financing Receivables 60 To 89 Days Past Due and Accruing | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	34	26
Commercial | Financing Receivables 60 To 89 Days Past Due and Accruing | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	23	0
Commercial | Financing Receivables 60 To 89 Days Past Due and Accruing | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	1
Commercial | Financing Receivables 90 Days or More Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	15	9
Commercial | Financing Receivables 90 Days or More Past Due and Accruing | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	13	9
Commercial | Financing Receivables 90 Days or More Past Due and Accruing | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	2	0
Commercial | Financing Receivables 90 Days or More Past Due and Accruing | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail
Financing Receivable, Past Due [Line Items]
Loans and leases	75,026	67,813
Loans and leases, nonaccrual	581	519
Loans and leases, nonaccrual with no related ACL	402	349
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	29,548	22,822
Loans and leases, nonaccrual	236	201
Loans and leases, nonaccrual with no related ACL	199	137
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	13,684	12,015
Loans and leases, nonaccrual	235	220
Loans and leases, nonaccrual with no related ACL	190	186
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	13,155	14,549
Loans and leases, nonaccrual	52	55
Loans and leases, nonaccrual with no related ACL	9	22
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	13,094	12,997
Loans and leases, nonaccrual	33	23
Loans and leases, nonaccrual with no related ACL	3	2
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,545	5,430
Loans and leases, nonaccrual	25	20
Loans and leases, nonaccrual with no related ACL	1	2
Retail | FHA, VA And USDA Loans
Financing Receivable, Past Due [Line Items]
Loans and leases, 90 days or more past due and still accruing	425	544
Retail | Current
Financing Receivable, Past Due [Line Items]
Loans and leases	73,548	66,244
Retail | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	28,779	21,918
Retail | Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	13,393	11,745
Retail | Current | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	12,934	14,324
Retail | Current | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	13,006	12,926
Retail | Current | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,436	5,331
Retail | Financing Receivables, 30 to 59 Days Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	309	345
Retail | Financing Receivables, 30 to 59 Days Past Due and Accruing | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	66	102
Retail | Financing Receivables, 30 to 59 Days Past Due and Accruing | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	41	38
Retail | Financing Receivables, 30 to 59 Days Past Due and Accruing | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	131	131
Retail | Financing Receivables, 30 to 59 Days Past Due and Accruing | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	32	34
Retail | Financing Receivables, 30 to 59 Days Past Due and Accruing | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	39	40
Retail | Financing Receivables 60 To 89 Days Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	141	139
Retail | Financing Receivables 60 To 89 Days Past Due and Accruing | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	42	52
Retail | Financing Receivables 60 To 89 Days Past Due and Accruing | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	15	12
Retail | Financing Receivables 60 To 89 Days Past Due and Accruing | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	38	39
Retail | Financing Receivables 60 To 89 Days Past Due and Accruing | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	19	13
Retail | Financing Receivables 60 To 89 Days Past Due and Accruing | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	27	23
Retail | Financing Receivables 90 Days or More Past Due and Accruing
Financing Receivable, Past Due [Line Items]
Loans and leases	447	566
Retail | Financing Receivables 90 Days or More Past Due and Accruing | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	425	549
Retail | Financing Receivables 90 Days or More Past Due and Accruing | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | Financing Receivables 90 Days or More Past Due and Accruing | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Retail | Financing Receivables 90 Days or More Past Due and Accruing | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	4	1
Retail | Financing Receivables 90 Days or More Past Due and Accruing | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 18	$ 16