ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Accruing and Nonaccruing Past Due Amounts (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 1,465	$ 1,356
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	433	204
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	364	84
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	53	110
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	16	10
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,032	1,152
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	200	316
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	103	148
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	272	285
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	36	40
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	36	45
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	252	194
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	80	71
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	37	36
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	16	17
Financing Receivables, 30 to 59 Days Past Due | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	38	48
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	404	383
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	36	9
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1	30
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1	9
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	366	335
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	53	54
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	23	32
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	57	60
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	14	14
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3	10
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	172	127
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	24	19
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	12	11
Financing Receivables, 30 to 59 Days Past Due | Loans and Leases | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8	8
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	116	124
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	6	8
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4	4
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2	3
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	1
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	110	116
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	12	16
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7	12
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	20	20
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5	6
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2	6
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	38	32
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	13	11
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9	9
Financing Receivables, 60 to 89 Days Past Due | Loans and Leases | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4	4
Financing Receivables, 90 Days or More Past Due | Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	389	148
Financing Receivables, 90 Days or More Past Due | Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	945	849
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	324	71
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	50	77
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	15	0
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	556	701
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	135	246
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	73	104
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	195	205
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	17	20
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	31	29
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	42	35
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	43	41
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	16	16
Financing Receivables, 90 Days or More Past Due | Loans and Leases | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 4	$ 5