ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	$ 0		$ (2)
Charge-offs Resulting from Modification	3		3
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	702	[1]	699	[1]
Pre-Modification Outstanding Recorded Investment	13	[1]	13	[1]
Post-Modification Outstanding Recorded Investment	13	[1]	13	[1]
Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	79	[2]	153	[2]
Pre-Modification Outstanding Recorded Investment	17	[2]	10	[2]
Post-Modification Outstanding Recorded Investment	17	[2]	9	[2]
Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1,140	[3]	1,094	[3]
Pre-Modification Outstanding Recorded Investment	45	[3]	48	[3]
Post-Modification Outstanding Recorded Investment	42	[3]	45	[3]
Commercial Banking
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(1)		(1)
Charge-offs Resulting from Modification	0		0
Commercial Banking | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	7	[1]	8	[1]
Pre-Modification Outstanding Recorded Investment	1	[1]	1	[1]
Post-Modification Outstanding Recorded Investment	1	[1]	1	[1]
Commercial Banking | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	28	[2]	13	[2]
Pre-Modification Outstanding Recorded Investment	10	[2]	1	[2]
Post-Modification Outstanding Recorded Investment	10	[2]	1	[2]
Commercial Banking | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	2	[3]	1	[3]
Pre-Modification Outstanding Recorded Investment	6	[3]	0	[3]
Post-Modification Outstanding Recorded Investment	6	[3]	0	[3]
Commercial
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(1)		(1)
Charge-offs Resulting from Modification	0		0
Commercial | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	6	[1]	7	[1]
Pre-Modification Outstanding Recorded Investment	1	[1]	1	[1]
Post-Modification Outstanding Recorded Investment	1	[1]	1	[1]
Commercial | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	28	[2]	13	[2]
Pre-Modification Outstanding Recorded Investment	10	[2]	1	[2]
Post-Modification Outstanding Recorded Investment	10	[2]	1	[2]
Commercial | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	[3]	1	[3]
Pre-Modification Outstanding Recorded Investment	2	[3]	0	[3]
Post-Modification Outstanding Recorded Investment	2	[3]	0	[3]
Commercial real estate
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0
Charge-offs Resulting from Modification	0
Commercial real estate | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	[1]	1	[1]
Pre-Modification Outstanding Recorded Investment	0	[1]	0	[1]
Post-Modification Outstanding Recorded Investment	0	[1]	0	[1]
Commercial real estate | 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]
Commercial real estate | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	[3]
Pre-Modification Outstanding Recorded Investment	4	[3]
Post-Modification Outstanding Recorded Investment	4	[3]
Retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	1		(1)
Charge-offs Resulting from Modification	3		3
Retail | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	695	[1]	691	[1]
Pre-Modification Outstanding Recorded Investment	12	[1]	12	[1]
Post-Modification Outstanding Recorded Investment	12	[1]	12	[1]
Retail | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	51	[2]	140	[2]
Pre-Modification Outstanding Recorded Investment	7	[2]	9	[2]
Post-Modification Outstanding Recorded Investment	7	[2]	8	[2]
Retail | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	1,138	[3]	1,093	[3]
Pre-Modification Outstanding Recorded Investment	39	[3]	48	[3]
Post-Modification Outstanding Recorded Investment	36	[3]	45	[3]
Residential mortgages
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	(1)		(1)
Charge-offs Resulting from Modification	0		0
Residential mortgages | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	33	[1]	42	[1]
Pre-Modification Outstanding Recorded Investment	6	[1]	6	[1]
Post-Modification Outstanding Recorded Investment	6	[1]	6	[1]
Residential mortgages | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	10	[2]	12	[2]
Pre-Modification Outstanding Recorded Investment	2	[2]	2	[2]
Post-Modification Outstanding Recorded Investment	2	[2]	1	[2]
Residential mortgages | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	64	[3]	132	[3]
Pre-Modification Outstanding Recorded Investment	6	[3]	15	[3]
Post-Modification Outstanding Recorded Investment	6	[3]	14	[3]
Home equity loans
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		0
Charge-offs Resulting from Modification	0		0
Home equity loans | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	21	[1]	31	[1]
Pre-Modification Outstanding Recorded Investment	1	[1]	2	[1]
Post-Modification Outstanding Recorded Investment	1	[1]	2	[1]
Home equity loans | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	37	[2]	58	[2]
Pre-Modification Outstanding Recorded Investment	5	[2]	3	[2]
Post-Modification Outstanding Recorded Investment	5	[2]	3	[2]
Home equity loans | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	197	[3]	210	[3]
Pre-Modification Outstanding Recorded Investment	10	[3]	14	[3]
Post-Modification Outstanding Recorded Investment	10	[3]	14	[3]
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		0
Charge-offs Resulting from Modification	1		2
Home equity lines of credit | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	0	[1]	1	[1]
Pre-Modification Outstanding Recorded Investment	0	[1]	0	[1]
Post-Modification Outstanding Recorded Investment	0	[1]	0	[1]
Home equity lines of credit | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	3	[2]	70	[2]
Pre-Modification Outstanding Recorded Investment	0	[2]	4	[2]
Post-Modification Outstanding Recorded Investment	0	[2]	4	[2]
Home equity lines of credit | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	135	[3]	81	[3]
Pre-Modification Outstanding Recorded Investment	8	[3]	6	[3]
Post-Modification Outstanding Recorded Investment	7	[3]	5	[3]
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0	[4]	0	[4]
Charge-offs Resulting from Modification	1	[4]	0	[4]
Home equity loans serviced by others | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	17	[1],[4]	14	[1],[4]
Pre-Modification Outstanding Recorded Investment	1	[1],[4]	1	[1],[4]
Post-Modification Outstanding Recorded Investment	1	[1],[4]	1	[1],[4]
Home equity loans serviced by others | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	0	[2],[4]	0	[2],[4]
Pre-Modification Outstanding Recorded Investment	0	[2],[4]	0	[2],[4]
Post-Modification Outstanding Recorded Investment	0	[2],[4]	0	[2],[4]
Home equity loans serviced by others | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	46	[3],[4]	46	[3],[4]
Pre-Modification Outstanding Recorded Investment	2	[3],[4]	3	[3],[4]
Post-Modification Outstanding Recorded Investment	2	[3],[4]	2	[3],[4]
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0	[4]	0	[4]
Charge-offs Resulting from Modification	0	[4]	0	[4]
Home equity lines of credit serviced by others | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts			2	[1],[4]
Pre-Modification Outstanding Recorded Investment			0	[1],[4]
Post-Modification Outstanding Recorded Investment			0	[1],[4]
Home equity lines of credit serviced by others | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts			0	[2],[4]
Pre-Modification Outstanding Recorded Investment			0	[2],[4]
Post-Modification Outstanding Recorded Investment			0	[2],[4]
Home equity lines of credit serviced by others | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	7	[3],[4]	13	[3],[4]
Pre-Modification Outstanding Recorded Investment	0	[3],[4]	0	[3],[4]
Post-Modification Outstanding Recorded Investment	0	[3],[4]	0	[3],[4]
Automobile
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		0
Charge-offs Resulting from Modification	1		1
Automobile | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	20	[1]	22	[1]
Pre-Modification Outstanding Recorded Investment	1	[1]	0	[1]
Post-Modification Outstanding Recorded Investment	1	[1]	0	[1]
Automobile | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	[2]	0	[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	297	[3]	145	[3]
Pre-Modification Outstanding Recorded Investment	5	[3]	2	[3]
Post-Modification Outstanding Recorded Investment	4	[3]	2	[3]
Student
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	2		0
Charge-offs Resulting from Modification	0		0
Student | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	381	[3]	457	[3]
Pre-Modification Outstanding Recorded Investment	8	[3]	8	[3]
Post-Modification Outstanding Recorded Investment	7	[3]	8	[3]
Credit cards | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts	604	[1]	577	[1]
Pre-Modification Outstanding Recorded Investment	3	[1]	3	[1]
Post-Modification Outstanding Recorded Investment	3	[1]	3	[1]
Credit cards | 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
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	0		0
Charge-offs Resulting from Modification	0		0
Other retail | Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts			2	[1]
Pre-Modification Outstanding Recorded Investment			0	[1]
Post-Modification Outstanding Recorded Investment			0	[1]
Other retail | Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts			0	[2]
Pre-Modification Outstanding Recorded Investment			0	[2]
Post-Modification Outstanding Recorded Investment			0	[2]
Other retail | Other
Financing Receivable, Modifications [Line Items]
Number of Contracts	11	[3]	9	[3]
Pre-Modification Outstanding Recorded Investment	0	[3]	0	[3]
Post-Modification Outstanding Recorded Investment	$ 0	[3]	$ 0	[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] 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.