ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015 USD ($) contract	Jun. 30, 2014 USD ($) contract	Jun. 30, 2015 USD ($) contract	Jun. 30, 2014 USD ($) contract
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		$ 2	$ (1)	$ 2	$ 0
Charge-offs Resulting from Modification		$ 1	$ 3	$ 4	$ 7
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	706	718	1,409	1,417
Pre-Modification Outstanding Recorded Investment	[1]	$ 9	$ 16	$ 23	$ 29
Post-Modification Outstanding Recorded Investment	[1]	$ 9	$ 16	$ 23	$ 29
Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	95	151	174	304
Pre-Modification Outstanding Recorded Investment	[2]	$ 15	$ 10	$ 32	$ 20
Post-Modification Outstanding Recorded Investment	[2]	$ 15	$ 9	$ 32	$ 18
Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	805	1,094	1,945	2,331
Pre-Modification Outstanding Recorded Investment	[3]	$ 28	$ 48	$ 73	$ 100
Post-Modification Outstanding Recorded Investment	[3]	27	45	69	94
Commercial Banking
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
Commercial Banking | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	7	9	15	17
Pre-Modification Outstanding Recorded Investment	[1]	$ 1	$ 6	$ 3	$ 7
Post-Modification Outstanding Recorded Investment	[1]	$ 1	$ 6	$ 3	$ 7
Commercial Banking | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	36	17	64	30
Pre-Modification Outstanding Recorded Investment	[2]	$ 2	$ 1	$ 12	$ 2
Post-Modification Outstanding Recorded Investment	[2]	$ 2	$ 1	$ 12	$ 2
Commercial Banking | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	3	1	5	2
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 6	$ 0
Post-Modification Outstanding Recorded Investment	[3]	0	0	6	0
Commercial
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
Commercial | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	7	8	14	15
Pre-Modification Outstanding Recorded Investment	[1]	$ 1	$ 6	$ 3	$ 7
Post-Modification Outstanding Recorded Investment	[1]	$ 1	$ 6	$ 3	$ 7
Commercial | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	36	15	64	28
Pre-Modification Outstanding Recorded Investment	[2]	$ 2	$ 1	$ 12	$ 2
Post-Modification Outstanding Recorded Investment	[2]	$ 2	$ 1	$ 12	$ 2
Commercial | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	3	1	4	2
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 2	$ 0
Post-Modification Outstanding Recorded Investment	[3]	0	0	2	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
Commercial real estate | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	0	1	1	2
Pre-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Commercial real estate | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0	2	0	2
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Commercial real estate | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	0	1	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 4	$ 0
Post-Modification Outstanding Recorded Investment	[3]	0	0	4	0
Retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		2	(1)	3	0
Charge-offs Resulting from Modification		$ 1	$ 3	$ 4	$ 7
Retail | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	699	709	1,394	1,400
Pre-Modification Outstanding Recorded Investment	[1]	$ 8	$ 10	$ 20	$ 22
Post-Modification Outstanding Recorded Investment	[1]	$ 8	$ 10	$ 20	$ 22
Retail | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	59	134	110	274
Pre-Modification Outstanding Recorded Investment	[2]	$ 13	$ 9	$ 20	$ 18
Post-Modification Outstanding Recorded Investment	[2]	$ 13	$ 8	$ 20	$ 16
Retail | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	802	1,093	1,940	2,329
Pre-Modification Outstanding Recorded Investment	[3]	$ 28	$ 48	$ 67	$ 100
Post-Modification Outstanding Recorded Investment	[3]	27	45	63	94
Residential mortgages
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	(1)	(1)	0
Charge-offs Resulting from Modification		$ 0	$ 0	$ 0	$ 0
Residential mortgages | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	20	24	53	66
Pre-Modification Outstanding Recorded Investment	[1]	$ 3	$ 4	$ 9	$ 10
Post-Modification Outstanding Recorded Investment	[1]	$ 3	$ 4	$ 9	$ 10
Residential mortgages | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	9	10	19	22
Pre-Modification Outstanding Recorded Investment	[2]	$ 2	$ 1	$ 4	$ 3
Post-Modification Outstanding Recorded Investment	[2]	$ 2	$ 2	$ 4	$ 3
Residential mortgages | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	42	132	106	239
Pre-Modification Outstanding Recorded Investment	[3]	$ 4	$ 15	$ 10	$ 28
Post-Modification Outstanding Recorded Investment	[3]	4	14	10	28
Home equity loans
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	0
Charge-offs Resulting from Modification		$ 0	$ 0	$ 0	$ 2
Home equity loans | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	26	37	47	68
Pre-Modification Outstanding Recorded Investment	[1]	$ 1	$ 2	$ 2	$ 4
Post-Modification Outstanding Recorded Investment	[1]	$ 1	$ 2	$ 2	$ 4
Home equity loans | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	49	10	86	68
Pre-Modification Outstanding Recorded Investment	[2]	$ 11	$ 1	$ 16	$ 4
Post-Modification Outstanding Recorded Investment	[2]	$ 11	$ 0	$ 16	$ 3
Home equity loans | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	97	210	294	523
Pre-Modification Outstanding Recorded Investment	[3]	$ 7	$ 14	$ 17	$ 34
Post-Modification Outstanding Recorded Investment	[3]	7	14	17	32
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		$ 1	$ 2	$ 2	$ 3
Home equity lines of credit | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	0	1	0	2
Pre-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Home equity lines of credit | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0	106	3	176
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 7	$ 0	$ 11
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 6	$ 0	$ 10
Home equity lines of credit | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	78	81	213	159
Pre-Modification Outstanding Recorded Investment	[3]	$ 5	$ 6	$ 14	$ 11
Post-Modification Outstanding Recorded Investment	[3]	5	5	12	9
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	[4]	0	0	0	0
Charge-offs Resulting from Modification	[4]	$ 0	$ 0	$ 1	$ 0
Home equity loans serviced by others | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	5	4	22	18
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 0	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 0	$ 1	$ 1
Home equity loans serviced by others | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2],[4]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[2],[4]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2],[4]	$ 0	$ 0	$ 0	$ 0
Home equity loans serviced by others | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3],[4]	25	46	71	85
Pre-Modification Outstanding Recorded Investment	[3],[4]	$ 1	$ 3	$ 3	$ 3
Post-Modification Outstanding Recorded Investment	[3],[4]	1	2	3	3
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	[4]	0	0	0	0
Charge-offs Resulting from Modification	[4]	$ 0	$ 0	$ 0	$ 0
Home equity lines of credit serviced by others | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	0	1	0	3
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 0	$ 0	$ 0
Home equity lines of credit serviced by others | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2],[4]	0	1	0	1
Pre-Modification Outstanding Recorded Investment	[2],[4]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2],[4]	$ 0	$ 0	$ 0	$ 0
Home equity lines of credit serviced by others | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3],[4]	15	13	22	24
Pre-Modification Outstanding Recorded Investment	[3],[4]	$ 1	$ 0	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[3],[4]	1	0	1	1
Automobile
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	0
Charge-offs Resulting from Modification		$ 0	$ 1	$ 1	$ 2
Automobile | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	18	33	38	55
Pre-Modification Outstanding Recorded Investment	[1]	$ 1	$ 1	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[1]	$ 1	$ 1	$ 1	$ 1
Automobile | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	1	7	2	7
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 0	$ 0
Automobile | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	172	145	469	417
Pre-Modification Outstanding Recorded Investment	[3]	$ 3	$ 2	$ 8	$ 6
Post-Modification Outstanding Recorded Investment	[3]	2	2	6	4
Student
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	0	3	0
Charge-offs Resulting from Modification		$ 0	$ 0	$ 0	$ 0
Student | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	0	0	0	0
Pre-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Student | Maturity Extension
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
Student | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	369	457	750	853
Pre-Modification Outstanding Recorded Investment	[3]	$ 7	$ 8	$ 14	$ 16
Post-Modification Outstanding Recorded Investment	[3]	7	8	14	16
Credit cards
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	0	1	0
Charge-offs Resulting from Modification		$ 0	$ 0	$ 0	$ 0
Credit cards | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	630	608	1,234	1,185
Pre-Modification Outstanding Recorded Investment	[1]	$ 3	$ 3	$ 7	$ 6
Post-Modification Outstanding Recorded Investment	[1]	$ 3	$ 3	$ 7	$ 6
Credit cards | Maturity Extension
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
Credit cards | Other
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 retail
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
Other retail | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	0	1	0	3
Pre-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1]	$ 0	$ 0	$ 0	$ 0
Other retail | Maturity Extension
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
Other retail | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	4	9	15	29
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 1
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0	$ 0	$ 1

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

[2] 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).

[3] 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.

[4] 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.