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, 2016 USD ($) contract	Jun. 30, 2015 USD ($) contract	Jun. 30, 2016 USD ($) contract	Jun. 30, 2015 USD ($) contract
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		$ 1	$ 2	$ 1	$ 2
Charge-offs Resulting from Modification		1	1	1	4
Commercial Banking
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	(1)	(1)
Charge-offs Resulting from Modification		0	0	0	0
Commercial
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	(1)	(1)
Charge-offs Resulting from Modification		0	0	0	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	2	2	3
Charge-offs Resulting from Modification		1	1	1	4
Residential mortgages
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0	0	(1)
Charge-offs Resulting from Modification		0	0	0	0
Home equity loans
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
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	0	2
Home equity loans 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	1
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	0	1	1
Student
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	1	2	3
Charge-offs Resulting from Modification		0	0	0	0
Credit cards
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	1	1	1
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	$ 0	$ 0	$ 0
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	615	706	1,216	1,409
Pre-Modification Outstanding Recorded Investment	[2]	$ 5	$ 9	$ 15	$ 23
Post-Modification Outstanding Recorded Investment	[2]	$ 5	$ 9	$ 15	$ 23
Interest Rate Reduction | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	3	7	8	15
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 1	$ 1	$ 3
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 1	$ 1	$ 3
Interest Rate Reduction | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	3	7	8	14
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 1	$ 1	$ 3
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 1	$ 1	$ 3
Interest Rate Reduction | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0	0	0	1
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]	612	699	1,208	1,394
Pre-Modification Outstanding Recorded Investment	[2]	$ 5	$ 8	$ 14	$ 20
Post-Modification Outstanding Recorded Investment	[2]	$ 5	$ 8	$ 14	$ 20
Interest Rate Reduction | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	3	20	25	53
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 3	$ 4	$ 9
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 3	$ 4	$ 9
Interest Rate Reduction | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	15	26	29	47
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1	$ 2	$ 2
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1	$ 2	$ 2
Interest Rate Reduction | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	6	0	13	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 1	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0	$ 1	$ 0
Interest Rate Reduction | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[2]	3	5	6	22
Pre-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 0	$ 0	$ 1
Post-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 0	$ 0	$ 1
Interest Rate Reduction | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[2]	2		2	0
Pre-Modification Outstanding Recorded Investment	[1],[2]	$ 0		$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[2]	$ 0		$ 0	$ 0
Interest Rate Reduction | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	30	18	51	38
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 1	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 1	$ 1	$ 1
Interest Rate Reduction | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0		0	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 0		$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0		$ 0	$ 0
Interest Rate Reduction | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	552	630	1,081	1,234
Pre-Modification Outstanding Recorded Investment	[2]	$ 3	$ 3	$ 6	$ 7
Post-Modification Outstanding Recorded Investment	[2]	$ 3	$ 3	$ 6	$ 7
Interest Rate Reduction | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	1		1	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 0		$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0		$ 0	$ 0
Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	73	95	146	174
Pre-Modification Outstanding Recorded Investment	[3]	$ 10	$ 15	$ 19	$ 32
Post-Modification Outstanding Recorded Investment	[3]	$ 10	$ 15	$ 19	$ 32
Maturity Extension | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	28	36	54	64
Pre-Modification Outstanding Recorded Investment	[3]	$ 4	$ 2	$ 8	$ 12
Post-Modification Outstanding Recorded Investment	[3]	$ 4	$ 2	$ 8	$ 12
Maturity Extension | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	28	36	54	64
Pre-Modification Outstanding Recorded Investment	[3]	$ 4	$ 2	$ 8	$ 12
Post-Modification Outstanding Recorded Investment	[3]	$ 4	$ 2	$ 8	$ 12
Maturity Extension | Commercial real estate
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 | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	45	59	92	110
Pre-Modification Outstanding Recorded Investment	[3]	$ 6	$ 13	$ 11	$ 20
Post-Modification Outstanding Recorded Investment	[3]	$ 6	$ 13	$ 11	$ 20
Maturity Extension | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	10	9	16	19
Pre-Modification Outstanding Recorded Investment	[3]	$ 2	$ 2	$ 3	$ 4
Post-Modification Outstanding Recorded Investment	[3]	$ 2	$ 2	$ 3	$ 4
Maturity Extension | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	21	49	37	86
Pre-Modification Outstanding Recorded Investment	[3]	$ 2	$ 11	$ 4	$ 16
Post-Modification Outstanding Recorded Investment	[3]	$ 2	$ 11	$ 4	$ 16
Maturity Extension | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	8	0	27	3
Pre-Modification Outstanding Recorded Investment	[3]	$ 1	$ 0	$ 3	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 1	$ 0	$ 3	$ 0
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]	3		4	0
Pre-Modification Outstanding Recorded Investment	[1],[3]	$ 1		$ 1	$ 0
Post-Modification Outstanding Recorded Investment	[1],[3]	$ 1		$ 1	$ 0
Maturity Extension | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	3	1	8	2
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
Pre-Modification Outstanding Recorded Investment	[3]	$ 0		$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 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
Pre-Modification Outstanding Recorded Investment	[3]	$ 0		$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0		$ 0	$ 0
Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	742	805	1,336	1,945
Pre-Modification Outstanding Recorded Investment	[4]	$ 48	$ 28	$ 93	$ 73
Post-Modification Outstanding Recorded Investment	[4]	$ 47	$ 27	$ 91	$ 69
Other | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	4	3	9	5
Pre-Modification Outstanding Recorded Investment	[4]	$ 20	$ 0	$ 41	$ 6
Post-Modification Outstanding Recorded Investment	[4]	$ 21	$ 0	$ 41	$ 6
Other | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	4	3	9	4
Pre-Modification Outstanding Recorded Investment	[4]	$ 20	$ 0	$ 41	$ 2
Post-Modification Outstanding Recorded Investment	[4]	$ 21	$ 0	$ 41	$ 2
Other | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	0	0	0	1
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 4
Post-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 4
Other | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	738	802	1,327	1,940
Pre-Modification Outstanding Recorded Investment	[4]	$ 28	$ 28	$ 52	$ 67
Post-Modification Outstanding Recorded Investment	[4]	$ 26	$ 27	$ 50	$ 63
Other | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	67	42	131	106
Pre-Modification Outstanding Recorded Investment	[4]	$ 7	$ 4	$ 15	$ 10
Post-Modification Outstanding Recorded Investment	[4]	$ 7	$ 4	$ 15	$ 10
Other | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	94	97	181	294
Pre-Modification Outstanding Recorded Investment	[4]	$ 5	$ 7	$ 11	$ 17
Post-Modification Outstanding Recorded Investment	[4]	$ 5	$ 7	$ 11	$ 17
Other | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	92	78	124	213
Pre-Modification Outstanding Recorded Investment	[4]	$ 6	$ 5	$ 8	$ 14
Post-Modification Outstanding Recorded Investment	[4]	$ 6	$ 5	$ 8	$ 12
Other | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	16	25	34	71
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 1	$ 1	$ 3
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 1	$ 1	$ 3
Other | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	5	15	13	22
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 1	$ 1	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 1	$ 0	$ 1
Other | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	348	172	539	469
Pre-Modification Outstanding Recorded Investment	[4]	$ 7	$ 3	$ 10	$ 8
Post-Modification Outstanding Recorded Investment	[4]	$ 6	$ 2	$ 9	$ 6
Other | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	111	369	297	750
Pre-Modification Outstanding Recorded Investment	[4]	$ 2	$ 7	$ 6	$ 14
Post-Modification Outstanding Recorded Investment	[4]	$ 2	$ 7	$ 6	$ 14
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]	5	4	8	15
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0	$ 0	$ 0

[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.