ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Recorded Investment in Retail Loans by Delinquency Status (Details) - Loans and Leases - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 1,416	$ 1,356
Total	105,467	99,042
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	14,314	12,905
Past Due	186	316
Total	14,602	13,318
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,803	2,245
Past Due	105	148
Total	2,027	2,557
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,638	13,982
Past Due	266	285
Total	14,271	14,674
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	718	886
Past Due	33	40
Total	796	986
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	168	296
Past Due	45	45
Total	238	389
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	12,911	12,670
Past Due	207	194
Total	14,063	13,828
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,804	4,175
Past Due	78	71
Total	5,997	4,359
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,563	1,554
Past Due	35	36
Total	1,644	1,634
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,385	1,013
Past Due	15	17
Total	1,440	1,083
Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	52,304	49,726
Total	55,078	52,828
Financing Receivables, 1 to 29 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	102	97
Financing Receivables, 1 to 29 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	119	164
Financing Receivables, 1 to 29 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	367	407
Financing Receivables, 1 to 29 Days Past Due | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	45	60
Financing Receivables, 1 to 29 Days Past Due | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	25	48
Financing Receivables, 1 to 29 Days Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	945	964
Financing Receivables, 1 to 29 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	115	113
Financing Receivables, 1 to 29 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	46	44
Financing Receivables, 1 to 29 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	40	53
Financing Receivables, 1 to 29 Days Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,804	1,950
Financing Receivables, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	315	383
Financing Receivables, 30 to 59 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	32	54
Financing Receivables, 30 to 59 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	17	32
Financing Receivables, 30 to 59 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	44	60
Financing Receivables, 30 to 59 Days Past Due | Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	11	14
Financing Receivables, 30 to 59 Days Past Due | 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 | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	129	127
Financing Receivables, 30 to 59 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	22	19
Financing Receivables, 30 to 59 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	11	11
Financing Receivables, 30 to 59 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	7	8
Financing Receivables, 30 to 59 Days Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	276	335
Financing Receivables 60 To 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	118	124
Financing Receivables 60 To 89 Days Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	17	16
Financing Receivables 60 To 89 Days Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8	12
Financing Receivables 60 To 89 Days Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	22	20
Financing Receivables 60 To 89 Days Past Due | 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 | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3	6
Financing Receivables 60 To 89 Days Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	31	32
Financing Receivables 60 To 89 Days Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	11	11
Financing Receivables 60 To 89 Days Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8	9
Financing Receivables 60 To 89 Days Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3	4
Financing Receivables 60 To 89 Days Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	108	116
Financing Receivables 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	983	849
Financing Receivables 90 Days or More Past Due | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	137	246
Financing Receivables 90 Days or More Past Due | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	80	104
Financing Receivables 90 Days or More Past Due | Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	200	205
Financing Receivables 90 Days or More Past Due | 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 | Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	39	29
Financing Receivables 90 Days or More Past Due | Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	47	35
Financing Receivables 90 Days or More Past Due | Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	45	41
Financing Receivables 90 Days or More Past Due | Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	16	16
Financing Receivables 90 Days or More Past Due | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5	5
Financing Receivables 90 Days or More Past Due | Total retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 586	$ 701