ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Troubled Debt Restructuring (Details) $ in Millions		3 Months Ended
		Mar. 31, 2016 USD ($) contract	Mar. 31, 2015 USD ($) contract
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		$ 0	$ 0
Charge-offs Resulting from Modification		18	3
Commercial Banking
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		(1)	(1)
Charge-offs Resulting from Modification		18	0
Commercial
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		(1)	(1)
Charge-offs Resulting from Modification		18	0
Commercial real estate
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0
Charge-offs Resulting from Modification		0	0
Retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	1
Charge-offs Resulting from Modification		0	3
Residential mortgages
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	(1)
Charge-offs Resulting from Modification		0	0
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 lines of credit
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0
Charge-offs Resulting from Modification		0	1
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification	[1]	0	0
Charge-offs Resulting from Modification	[1]	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
Charge-offs Resulting from Modification	[1]	0	0
Automobile
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0
Charge-offs Resulting from Modification		0	1
Student
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		1	2
Charge-offs Resulting from Modification		0	0
Credit cards
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0
Charge-offs Resulting from Modification		0
Other retail
Financing Receivable, Modifications [Line Items]
Net Change to ALLL Resulting from Modification		0	0
Charge-offs Resulting from Modification		$ 0	$ 0
Interest Rate Reduction
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	601	702
Pre-Modification Outstanding Recorded Investment	[2]	$ 10	$ 13
Post-Modification Outstanding Recorded Investment	[2]	$ 10	$ 13
Interest Rate Reduction | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	5	7
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Interest Rate Reduction | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	5	6
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Interest Rate Reduction | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0	1
Pre-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0	$ 0
Interest Rate Reduction | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	596	695
Pre-Modification Outstanding Recorded Investment	[2]	$ 9	$ 12
Post-Modification Outstanding Recorded Investment	[2]	$ 9	$ 12
Interest Rate Reduction | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	22	33
Pre-Modification Outstanding Recorded Investment	[2]	$ 3	$ 6
Post-Modification Outstanding Recorded Investment	[2]	$ 3	$ 6
Interest Rate Reduction | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	14	21
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Interest Rate Reduction | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	7	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 0
Interest Rate Reduction | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[2]	3	17
Pre-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 1
Post-Modification Outstanding Recorded Investment	[1],[2]	$ 0	$ 1
Interest Rate Reduction | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[2]	0
Pre-Modification Outstanding Recorded Investment	[1],[2]	$ 0
Post-Modification Outstanding Recorded Investment	[1],[2]	$ 0
Interest Rate Reduction | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	21	20
Pre-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Post-Modification Outstanding Recorded Investment	[2]	$ 1	$ 1
Interest Rate Reduction | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0
Interest Rate Reduction | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	529	604
Pre-Modification Outstanding Recorded Investment	[2]	$ 3	$ 3
Post-Modification Outstanding Recorded Investment	[2]	$ 3	$ 3
Interest Rate Reduction | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[2]	0
Pre-Modification Outstanding Recorded Investment	[2]	$ 0
Post-Modification Outstanding Recorded Investment	[2]	$ 0
Maturity Extension
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	73	79
Pre-Modification Outstanding Recorded Investment	[3]	$ 9	$ 17
Post-Modification Outstanding Recorded Investment	[3]	$ 9	$ 17
Maturity Extension | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	26	28
Pre-Modification Outstanding Recorded Investment	[3]	$ 4	$ 10
Post-Modification Outstanding Recorded Investment	[3]	$ 4	$ 10
Maturity Extension | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	26	28
Pre-Modification Outstanding Recorded Investment	[3]	$ 4	$ 10
Post-Modification Outstanding Recorded Investment	[3]	$ 4	$ 10
Maturity Extension | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0
Maturity Extension | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	47	51
Pre-Modification Outstanding Recorded Investment	[3]	$ 5	$ 7
Post-Modification Outstanding Recorded Investment	[3]	$ 5	$ 7
Maturity Extension | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	6	10
Pre-Modification Outstanding Recorded Investment	[3]	$ 1	$ 2
Post-Modification Outstanding Recorded Investment	[3]	$ 1	$ 2
Maturity Extension | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	16	37
Pre-Modification Outstanding Recorded Investment	[3]	$ 2	$ 5
Post-Modification Outstanding Recorded Investment	[3]	$ 2	$ 5
Maturity Extension | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	19	3
Pre-Modification Outstanding Recorded Investment	[3]	$ 2	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 2	$ 0
Maturity Extension | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[3]	0	0
Pre-Modification Outstanding Recorded Investment	[1],[3]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[3]	$ 0	$ 0
Maturity Extension | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[3]	1
Pre-Modification Outstanding Recorded Investment	[1],[3]	$ 0
Post-Modification Outstanding Recorded Investment	[1],[3]	$ 0
Maturity Extension | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	5	1
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0
Maturity Extension | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0
Maturity Extension | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0	$ 0
Maturity Extension | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[3]	0
Pre-Modification Outstanding Recorded Investment	[3]	$ 0
Post-Modification Outstanding Recorded Investment	[3]	$ 0
Other
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	594	1,140
Pre-Modification Outstanding Recorded Investment	[4]	$ 45	$ 45
Post-Modification Outstanding Recorded Investment	[4]	$ 44	$ 42
Other | Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	5	2
Pre-Modification Outstanding Recorded Investment	[4]	$ 21	$ 6
Post-Modification Outstanding Recorded Investment	[4]	$ 20	$ 6
Other | Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	5	1
Pre-Modification Outstanding Recorded Investment	[4]	$ 21	$ 2
Post-Modification Outstanding Recorded Investment	[4]	$ 20	$ 2
Other | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	0	1
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 4
Post-Modification Outstanding Recorded Investment	[4]	$ 0	$ 4
Other | Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	589	1,138
Pre-Modification Outstanding Recorded Investment	[4]	$ 24	$ 39
Post-Modification Outstanding Recorded Investment	[4]	$ 24	$ 36
Other | Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	64	64
Pre-Modification Outstanding Recorded Investment	[4]	$ 8	$ 6
Post-Modification Outstanding Recorded Investment	[4]	$ 8	$ 6
Other | Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	87	197
Pre-Modification Outstanding Recorded Investment	[4]	$ 6	$ 10
Post-Modification Outstanding Recorded Investment	[4]	$ 6	$ 10
Other | Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	32	135
Pre-Modification Outstanding Recorded Investment	[4]	$ 2	$ 8
Post-Modification Outstanding Recorded Investment	[4]	$ 2	$ 7
Other | Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	18	46
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 1	$ 2
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 1	$ 2
Other | Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1],[4]	8	7
Pre-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[1],[4]	$ 0	$ 0
Other | Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	191	297
Pre-Modification Outstanding Recorded Investment	[4]	$ 3	$ 5
Post-Modification Outstanding Recorded Investment	[4]	$ 3	$ 4
Other | Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	186	381
Pre-Modification Outstanding Recorded Investment	[4]	$ 4	$ 8
Post-Modification Outstanding Recorded Investment	[4]	$ 4	$ 7
Other | Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	0
Pre-Modification Outstanding Recorded Investment	[4]	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 0
Other | Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[4]	3	11
Pre-Modification Outstanding Recorded Investment	[4]	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	[4]	$ 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.