ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($) contract	Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($) contract
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		$ 1	$ (1)	$ 3	$ (11)
Charge-offs Resulting from Modification		2	4	6	11
Commercial Banking
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	(1)	(8)
Charge-offs Resulting from Modification		1	0	1	0
Commercial
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	(1)	(8)
Charge-offs Resulting from Modification		1	0	1	0
Commercial real estate
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	0
Charge-offs Resulting from Modification		0	0	0	0
Retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	(1)	4	(3)
Charge-offs Resulting from Modification		1	4	5	11
Residential mortgages
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	(1)	(1)	(3)
Charge-offs Resulting from Modification		0	1	0	1
Home equity loans
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	(1)
Charge-offs Resulting from Modification		0	0	0	2
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	0
Charge-offs Resulting from Modification		0	1	2	4
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	[1]	0	(1)	0	(1)
Charge-offs Resulting from Modification	[1]	0	0	1	0
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	[1]	0	0	0	0
Charge-offs Resulting from Modification	[1]	0	0	0	0
Automobile
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	0
Charge-offs Resulting from Modification		1	1	2	3
Student
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	1	4	2
Charge-offs Resulting from Modification		0	0	0	0
Credit cards
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	1	0
Charge-offs Resulting from Modification		0	0	0	0
Other retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	0
Charge-offs Resulting from Modification		$ 0	$ 1	$ 0	$ 1
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	643	591	2,052	2,008
Pre-Modification Outstanding Recorded Investment	[2]	$ 9	$ 9	$ 32	$ 38
Post-Modification Outstanding Recorded Investment	[2]	$ 10	$ 10	$ 33	$ 39
Interest Rate Reduction | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	4	6	19	23
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 3	$ 7
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 3	$ 7
Interest Rate Reduction | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	4	5	18	20
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 3	$ 7
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 3	$ 7
Interest Rate Reduction | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0	1	1	3
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Interest Rate Reduction | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	639	585	2,033	1,985
Pre-Modification Outstanding Recorded Investment	[2]	$ 9	$ 9	$ 29	$ 31
Post-Modification Outstanding Recorded Investment	[2]	$ 10	$ 10	$ 30	$ 32
Interest Rate Reduction | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	24	28	77	94
Pre-Modification Outstanding Recorded Investment	[2]	$ 4	$ 4	$ 13	$ 14
Post-Modification Outstanding Recorded Investment	[2]	$ 4	$ 4	$ 13	$ 14
Interest Rate Reduction | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	30	24	77	92
Pre-Modification Outstanding Recorded Investment	[2]	$ 2	$ 2	$ 4	$ 6
Post-Modification Outstanding Recorded Investment	[2]	$ 2	$ 3	$ 4	$ 7
Interest Rate Reduction | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	1	5	1	7
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Interest Rate Reduction | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[2]	2	8	24	26
Pre-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 0	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 0	$ 1	$ 1
Interest Rate Reduction | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[2]	0	0	0	3
Pre-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 0	$ 0	$ 0
Interest Rate Reduction | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	33	7	71	62
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 0	$ 2	$ 1
Interest Rate Reduction | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Interest Rate Reduction | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	547	513	1,781	1,698
Pre-Modification Outstanding Recorded Investment	[2]	$ 3	$ 3	$ 10	$ 9
Post-Modification Outstanding Recorded Investment	[2]	$ 3	$ 3	$ 10	$ 9
Interest Rate Reduction | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	2	0	2	3
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	135	104	309	408
Pre-Modification Outstanding Recorded Investment	[3]	$ 22	$ 9	$ 54	$ 29
Post-Modification Outstanding Recorded Investment	[3]	$ 22	$ 9	$ 54	$ 27
Maturity Extension | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	50	13	114	43
Pre-Modification Outstanding Recorded Investment	[3]	$ 7	$ 3	$ 19	$ 5
Post-Modification Outstanding Recorded Investment	[3]	$ 7	$ 3	$ 19	$ 5
Maturity Extension | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	50	10	114	38
Pre-Modification Outstanding Recorded Investment	[3]	$ 7	$ 2	$ 19	$ 4
Post-Modification Outstanding Recorded Investment	[3]	$ 7	$ 2	$ 19	$ 4
Maturity Extension | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	3	0	5
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 1	$ 0	$ 1
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 1	$ 0	$ 1
Maturity Extension | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	85	91	195	365
Pre-Modification Outstanding Recorded Investment	[3]	$ 15	$ 6	$ 35	$ 24
Post-Modification Outstanding Recorded Investment	[3]	$ 15	$ 6	$ 35	$ 22
Maturity Extension | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	8	10	27	32
Pre-Modification Outstanding Recorded Investment	[3]	$ 1	$ 2	$ 5	$ 5
Post-Modification Outstanding Recorded Investment	[3]	$ 1	$ 1	$ 5	$ 4
Maturity Extension | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	72	8	158	76
Pre-Modification Outstanding Recorded Investment	[3]	$ 14	$ 0	$ 30	$ 4
Post-Modification Outstanding Recorded Investment	[3]	$ 14	$ 2	$ 30	$ 5
Maturity Extension | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	2	69	5	245
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 4	$ 0	$ 15
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 3	$ 0	$ 13
Maturity Extension | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[3]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[1],[3]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[3]	$ 0	$ 0	$ 0	$ 0
Maturity Extension | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[3]	0	0	0	1
Pre-Modification Outstanding Recorded Investment	[1],[3]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[3]	$ 0	$ 0	$ 0	$ 0
Maturity Extension | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	3	4	5	11
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Maturity Extension | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Maturity Extension | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Maturity Extension | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 0
Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	604	1,112	2,549	3,443
Pre-Modification Outstanding Recorded Investment	[4]	$ 56	$ 47	$ 129	$ 147
Post-Modification Outstanding Recorded Investment	[4]	$ 55	$ 43	$ 124	$ 137
Other | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	8	3	13	5
Pre-Modification Outstanding Recorded Investment	[4]	$ 28	$ 0	$ 34	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 28	$ 0	$ 34	$ 0
Other | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	8	3	12	5
Pre-Modification Outstanding Recorded Investment	[4]	$ 28	$ 0	$ 30	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 28	$ 0	$ 30	$ 0
Other | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	0	0	1	0
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 4	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 4	$ 0
Other | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	596	1,109	2,536	3,438
Pre-Modification Outstanding Recorded Investment	[4]	$ 28	$ 47	$ 95	$ 147
Post-Modification Outstanding Recorded Investment	[4]	$ 27	$ 43	$ 90	$ 137
Other | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	78	102	184	341
Pre-Modification Outstanding Recorded Investment	[4]	$ 9	$ 12	$ 19	$ 40
Post-Modification Outstanding Recorded Investment	[4]	$ 9	$ 11	$ 19	$ 39
Other | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	85	266	379	789
Pre-Modification Outstanding Recorded Investment	[4]	$ 8	$ 15	$ 25	$ 49
Post-Modification Outstanding Recorded Investment	[4]	$ 7	$ 15	$ 24	$ 47
Other | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	58	98	271	257
Pre-Modification Outstanding Recorded Investment	[4]	$ 4	$ 7	$ 18	$ 18
Post-Modification Outstanding Recorded Investment	[4]	$ 3	$ 6	$ 15	$ 15
Other | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	26	26	97	111
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 2	$ 1	$ 5	$ 4
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 1	$ 1	$ 4	$ 4
Other | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	12	9	34	33
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 1	$ 1	$ 2	$ 2
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 1	$ 1	$ 2	$ 2
Other | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	182	256	651	673
Pre-Modification Outstanding Recorded Investment	[4]	$ 2	$ 5	$ 10	$ 11
Post-Modification Outstanding Recorded Investment	[4]	$ 3	$ 3	$ 9	$ 7
Other | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	151	346	901	1,199
Pre-Modification Outstanding Recorded Investment	[4]	$ 2	$ 6	$ 16	$ 22
Post-Modification Outstanding Recorded Investment	[4]	$ 3	$ 6	$ 17	$ 22
Other | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 0
Other | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	4	6	19	35
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 1
Post-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 1

[1] The Company’s SBO portfolio consists of purchased home equity loans and lines that were originally serviced by others. The Company now services a portion of this portfolio internally.

[2] Includes modifications that consist of multiple concessions, one of which is an interest rate reduction.

[3] Includes modifications that consist of multiple concessions, one of which is a maturity extension (unless one of the other concessions was an interest rate reduction).

[4] Includes modifications other than interest rate reductions or maturity extensions, such as lowering scheduled payments for a specified period of time, principal forbearance, capitalizing arrearages, and principal forgiveness. Also included are the following: deferrals, trial modifications, certain bankruptcies, loans in forbearance and prepayment plans. Modifications can include the deferral of accrued interest resulting in post-modification balances being higher than pre-modification.