ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	$ 1		$ 5		$ (68)
Charge-offs Resulting from Modification	16		32		84
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	2,581	[1]	3,573	[1]	3,596	[1]
Pre-Modification Outstanding Recorded Investment	49	[1]	87	[1]	136	[1]
Post-Modification Outstanding Recorded Investment	50	[1]	89	[1]	139	[1]
Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	566	[2]	2,366	[2]	314	[2]
Pre-Modification Outstanding Recorded Investment	52	[2]	110	[2]	54	[2]
Post-Modification Outstanding Recorded Investment	51	[2]	101	[2]	53	[2]
Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	4,771	[3]	6,606	[3]	18,689	[3]
Pre-Modification Outstanding Recorded Investment	251	[3]	253	[3]	771	[3]
Post-Modification Outstanding Recorded Investment	262	[3]	232	[3]	709	[3]
Commercial Banking
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	3		(2)		(55)
Charge-offs Resulting from Modification	3		1		16
Commercial Banking | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	34	[1]	137	[1]	22	[1]
Pre-Modification Outstanding Recorded Investment	9	[1]	20	[1]	22	[1]
Post-Modification Outstanding Recorded Investment	9	[1]	20	[1]	22	[1]
Commercial Banking | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	146	[2]	137	[2]	114	[2]
Pre-Modification Outstanding Recorded Investment	24	[2]	19	[2]	39	[2]
Post-Modification Outstanding Recorded Investment	24	[2]	19	[2]	37	[2]
Commercial Banking | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	28	[3]	7	[3]	196	[3]
Pre-Modification Outstanding Recorded Investment	59	[3]	1	[3]	115	[3]
Post-Modification Outstanding Recorded Investment	81	[3]	1	[3]	120	[3]
Commercial
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	3		0		(29)
Charge-offs Resulting from Modification	0		1		14
Commercial | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	25	[1]	126	[1]	18	[1]
Pre-Modification Outstanding Recorded Investment	8	[1]	13	[1]	13	[1]
Post-Modification Outstanding Recorded Investment	7	[1]	13	[1]	13	[1]
Commercial | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	131	[2]	134	[2]	108	[2]
Pre-Modification Outstanding Recorded Investment	21	[2]	18	[2]	25	[2]
Post-Modification Outstanding Recorded Investment	22	[2]	18	[2]	24	[2]
Commercial | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	27	[3]	6	[3]	180	[3]
Pre-Modification Outstanding Recorded Investment	52	[3]	1	[3]	43	[3]
Post-Modification Outstanding Recorded Investment	74	[3]	1	[3]	46	[3]
Commercial real estate
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		(2)		(26)
Charge-offs Resulting from Modification	3		0		2
Commercial real estate | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	9	[1]	11	[1]	4	[1]
Pre-Modification Outstanding Recorded Investment	1	[1]	7	[1]	9	[1]
Post-Modification Outstanding Recorded Investment	2	[1]	7	[1]	9	[1]
Commercial real estate | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	15	[2]	3	[2]	6	[2]
Pre-Modification Outstanding Recorded Investment	3	[2]	1	[2]	14	[2]
Post-Modification Outstanding Recorded Investment	2	[2]	1	[2]	13	[2]
Commercial real estate | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	[3]	1	[3]	16	[3]
Pre-Modification Outstanding Recorded Investment	7	[3]	0	[3]	72	[3]
Post-Modification Outstanding Recorded Investment	7	[3]	0	[3]	74	[3]
Retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(2)		7		(13)
Charge-offs Resulting from Modification	13		31		68
Retail | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	2,547	[1]	3,436	[1]	3,574	[1]
Pre-Modification Outstanding Recorded Investment	40	[1]	67	[1]	114	[1]
Post-Modification Outstanding Recorded Investment	41	[1]	69	[1]	117	[1]
Retail | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	420	[2]	2,229	[2]	200	[2]
Pre-Modification Outstanding Recorded Investment	28	[2]	91	[2]	15	[2]
Post-Modification Outstanding Recorded Investment	27	[2]	82	[2]	16	[2]
Retail | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	4,743	[3]	6,599	[3]	18,493	[3]
Pre-Modification Outstanding Recorded Investment	192	[3]	252	[3]	656	[3]
Post-Modification Outstanding Recorded Investment	181	[3]	231	[3]	589	[3]
Residential mortgages
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(4)		5		(4)	[4]
Charge-offs Resulting from Modification	1		2		9
Residential mortgages | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	126	[1]	200	[1]	346	[1]
Pre-Modification Outstanding Recorded Investment	17	[1]	32	[1]	77	[1]
Post-Modification Outstanding Recorded Investment	17	[1]	33	[1]	80	[1]
Residential mortgages | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	40	[2]	46	[2]	36	[2]
Pre-Modification Outstanding Recorded Investment	6	[2]	5	[2]	4	[2]
Post-Modification Outstanding Recorded Investment	5	[2]	6	[2]	5	[2]
Residential mortgages | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	393	[3]	430	[3]	2,331	[3]
Pre-Modification Outstanding Recorded Investment	47	[3]	64	[3]	203	[3]
Post-Modification Outstanding Recorded Investment	46	[3]	63	[3]	195	[3]
Home equity loans
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(1)		2		(2)	[4]
Charge-offs Resulting from Modification	2		5		14
Home equity loans | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	125	[1]	196	[1]	218	[1]
Pre-Modification Outstanding Recorded Investment	8	[1]	15	[1]	18	[1]
Post-Modification Outstanding Recorded Investment	9	[1]	16	[1]	19	[1]
Home equity loans | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	85	[2]	94	[2]	48	[2]
Pre-Modification Outstanding Recorded Investment	5	[2]	6	[2]	4	[2]
Post-Modification Outstanding Recorded Investment	6	[2]	6	[2]	5	[2]
Home equity loans | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1,046	[3]	995	[3]	2,336	[3]
Pre-Modification Outstanding Recorded Investment	63	[3]	57	[3]	130	[3]
Post-Modification Outstanding Recorded Investment	62	[3]	51	[3]	117	[3]
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		0		0	[4]
Charge-offs Resulting from Modification	5		16		20
Home equity lines of credit | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	7	[1]	18	[1]	1	[1]
Pre-Modification Outstanding Recorded Investment	0	[1]	1	[1]	0	[1]
Post-Modification Outstanding Recorded Investment	0	[1]	1	[1]	0	[1]
Home equity lines of credit | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	276	[2]	2,081	[2]	109	[2]
Pre-Modification Outstanding Recorded Investment	17	[2]	80	[2]	6	[2]
Post-Modification Outstanding Recorded Investment	16	[2]	70	[2]	6	[2]
Home equity lines of credit | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	356	[3]	771	[3]	1,554	[3]
Pre-Modification Outstanding Recorded Investment	25	[3]	53	[3]	92	[3]
Post-Modification Outstanding Recorded Investment	21	[3]	46	[3]	72	[3]
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(1)	[5]	0	[5]	(8)	[4],[5]
Charge-offs Resulting from Modification	0	[5]	3	[5]	13	[5]
Home equity loans serviced by others | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	42	[1],[5]	31	[1],[5]	41	[1],[5]
Pre-Modification Outstanding Recorded Investment	2	[1],[5]	2	[1],[5]	2	[1],[5]
Post-Modification Outstanding Recorded Investment	2	[1],[5]	2	[1],[5]	2	[1],[5]
Home equity loans serviced by others | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	0	[2],[5]	5	[2],[5]	7	[2],[5]
Pre-Modification Outstanding Recorded Investment	0	[2],[5]	0	[2],[5]	1	[2],[5]
Post-Modification Outstanding Recorded Investment	0	[2],[5]	0	[2],[5]	0	[2],[5]
Home equity loans serviced by others | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	138	[3],[5]	269	[3],[5]	1,192	[3],[5]
Pre-Modification Outstanding Recorded Investment	5	[3],[5]	12	[3],[5]	50	[3],[5]
Post-Modification Outstanding Recorded Investment	5	[3],[5]	10	[3],[5]	37	[3],[5]
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0	[5]	0	[5]	0	[4],[5]
Charge-offs Resulting from Modification	0	[5]	1	[5]	4	[5]
Home equity lines of credit serviced by others | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	4	[1],[5]	3	[1],[5]	3	[1],[5]
Pre-Modification Outstanding Recorded Investment	0	[1],[5]	0	[1],[5]	0	[1],[5]
Post-Modification Outstanding Recorded Investment	0	[1],[5]	0	[1],[5]	0	[1],[5]
Home equity lines of credit serviced by others | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	[2],[5]	1	[2],[5]	0	[2],[5]
Pre-Modification Outstanding Recorded Investment	0	[2],[5]	0	[2],[5]	0	[2],[5]
Post-Modification Outstanding Recorded Investment	0	[2],[5]	0	[2],[5]	0	[2],[5]
Home equity lines of credit serviced by others | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	39	[3],[5]	43	[3],[5]	322	[3],[5]
Pre-Modification Outstanding Recorded Investment	2	[3],[5]	2	[3],[5]	17	[3],[5]
Post-Modification Outstanding Recorded Investment	2	[3],[5]	1	[3],[5]	13	[3],[5]
Automobile
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		0		(4)	[4]
Charge-offs Resulting from Modification	5		3		4
Automobile | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	75	[1]	238	[1]
Pre-Modification Outstanding Recorded Investment	1	[1]	2	[1]
Post-Modification Outstanding Recorded Investment	1	[1]	2	[1]
Automobile | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	18	[2]	2	[2]
Pre-Modification Outstanding Recorded Investment	0	[2]	0	[2]
Post-Modification Outstanding Recorded Investment	0	[2]	0	[2]
Automobile | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1,039	[3]	1,323	[3]	2,938	[3]
Pre-Modification Outstanding Recorded Investment	17	[3]	13	[3]	19	[3]
Post-Modification Outstanding Recorded Investment	13	[3]	10	[3]	14	[3]
Student
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	5		0		3	[4]
Charge-offs Resulting from Modification	0		0		0
Student | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1,675	[3]	2,620	[3]	7,557	[3]
Pre-Modification Outstanding Recorded Investment	31	[3]	48	[3]	139	[3]
Post-Modification Outstanding Recorded Investment	31	[3]	47	[3]	138	[3]
Credit cards
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification					2	[4]
Charge-offs Resulting from Modification					0
Credit cards | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	2,165	[1]	2,729	[1]	2,965	[1]
Pre-Modification Outstanding Recorded Investment	12	[1]	15	[1]	17	[1]
Post-Modification Outstanding Recorded Investment	12	[1]	15	[1]	16	[1]
Credit cards | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	0	[2]	0	[2]	0	[2]
Pre-Modification Outstanding Recorded Investment	0	[2]	0	[2]	0	[2]
Post-Modification Outstanding Recorded Investment	0	[2]	0	[2]	0	[2]
Credit cards | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts					0	[3]
Pre-Modification Outstanding Recorded Investment					0	[3]
Post-Modification Outstanding Recorded Investment					0	[3]
Other retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(1)		0		0	[4]
Charge-offs Resulting from Modification	0		1		4
Other retail | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	3	[1]	21	[1]
Pre-Modification Outstanding Recorded Investment	0	[1]	0	[1]
Post-Modification Outstanding Recorded Investment	0	[1]	0	[1]
Other retail | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	0	[2]	0	[2]
Pre-Modification Outstanding Recorded Investment	0	[2]	0	[2]
Post-Modification Outstanding Recorded Investment	0	[2]	0	[2]
Other retail | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	57	[3]	148	[3]	263	[3]
Pre-Modification Outstanding Recorded Investment	2	[3]	3	[3]	6	[3]
Post-Modification Outstanding Recorded Investment	$ 1	[3]	$ 3	[3]	$ 3	[3]

[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] Retail data is estimated for certain loan classes.

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