ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Loans and leases	$ 156,172	$ 128,163
Loans and leases, nonaccrual	839	702
Loans and leases, nonaccrual with no related ACL	438	386
Financial Asset, 1 to 29 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	153,985	126,308
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	502	412
Financing Receivables 60 To 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	134	166
Financing Receivables 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	712	575
Commercial
Financing Receivable, Past Due [Line Items]
Loans and leases	81,445	60,350
Loans and leases, nonaccrual	239	183
Loans and leases, nonaccrual with no related ACL	31	37
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	51,801	44,500
Loans and leases, nonaccrual	202	171
Loans and leases, nonaccrual with no related ACL	24	36
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	28,070	14,264
Loans and leases, nonaccrual	37	11
Loans and leases, nonaccrual with no related ACL	7	1
Commercial | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,574	1,586
Loans and leases, nonaccrual	0	1
Loans and leases, nonaccrual with no related ACL	0	0
Commercial | Financial Asset, 1 to 29 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	80,895	60,064
Commercial | Financial Asset, 1 to 29 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	51,514	44,247
Commercial | Financial Asset, 1 to 29 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	27,827	14,247
Commercial | Financial Asset, 1 to 29 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	1,554	1,570
Commercial | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	226	67
Commercial | Financing Receivables, 30 to 59 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	37	47
Commercial | Financing Receivables, 30 to 59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	172	6
Commercial | Financing Receivables, 30 to 59 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	17	14
Commercial | Financing Receivables 60 To 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	13	27
Commercial | Financing Receivables 60 To 89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	9	26
Commercial | Financing Receivables 60 To 89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	1	0
Commercial | Financing Receivables 60 To 89 Days Past Due | Leases
Financing Receivable, Past Due [Line Items]
Loans and leases	3	1
Commercial | Financing Receivables 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	72	9
Commercial | Financing Receivables 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans and leases	39	9
Commercial | Financing Receivables 90 Days or More Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans and leases	33	0
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	74,727	67,813
Loans and leases, nonaccrual	600	519
Loans and leases, nonaccrual with no related ACL	407	349
Retail | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	29,088	22,822
Loans and leases, nonaccrual with no related ACL	208	137
Retail | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	13,122	12,015
Loans and leases, nonaccrual with no related ACL	186	186
Retail | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	13,868	14,549
Loans and leases, nonaccrual with no related ACL	9	22
Retail | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	13,141	12,997
Loans and leases, nonaccrual with no related ACL	3	2
Retail | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,508	5,430
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	623	544
Retail | Financial Asset, 1 to 29 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	73,090	66,244
Retail | Financial Asset, 1 to 29 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	28,119	21,918
Retail | Financial Asset, 1 to 29 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	12,834	11,745
Retail | Financial Asset, 1 to 29 Days Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	13,660	14,324
Retail | Financial Asset, 1 to 29 Days Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	13,068	12,926
Retail | Financial Asset, 1 to 29 Days Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	5,409	5,331
Retail | Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	276	345
Retail | Financing Receivables, 30 to 59 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	59	102
Retail | Financing Receivables, 30 to 59 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	36	38
Retail | Financing Receivables, 30 to 59 Days Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	120	131
Retail | Financing Receivables, 30 to 59 Days Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	26	34
Retail | Financing Receivables, 30 to 59 Days Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	35	40
Retail | Financing Receivables 60 To 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	121	139
Retail | Financing Receivables 60 To 89 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	34	52
Retail | Financing Receivables 60 To 89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	12	12
Retail | Financing Receivables 60 To 89 Days Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	38	39
Retail | Financing Receivables 60 To 89 Days Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	13	13
Retail | Financing Receivables 60 To 89 Days Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	24	23
Retail | Financing Receivables 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Loans and leases	640	566
Retail | Financing Receivables 90 Days or More Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Loans and leases	623	549
Loans and leases, nonaccrual	253	201
Retail | Financing Receivables 90 Days or More Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Loans and leases, nonaccrual	240	220
Retail | Financing Receivables 90 Days or More Past Due | Automobile
Financing Receivable, Past Due [Line Items]
Loans and leases	0	0
Loans and leases, nonaccrual	50	55
Retail | Financing Receivables 90 Days or More Past Due | Education
Financing Receivable, Past Due [Line Items]
Loans and leases	3	1
Loans and leases, nonaccrual	31	23
Retail | Financing Receivables 90 Days or More Past Due | Other retail
Financing Receivable, Past Due [Line Items]
Loans and leases	14	16
Loans and leases, nonaccrual	$ 26	$ 20