ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Default of Modified Debt Agreements (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]
Number of Contracts | contract		283	512	638	1,064
Balance Defaulted		$ 11	$ 25	$ 26	$ 44
Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		8	6	14	18
Balance Defaulted		$ 1	$ 2	$ 1	$ 4
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		8	6	14	17
Balance Defaulted		$ 1	$ 2	$ 1	$ 3
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		0	0	0	1
Balance Defaulted		$ 0	$ 0	$ 0	$ 1
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		275	506	624	1,046
Balance Defaulted		$ 10	$ 23	$ 25	$ 40
Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		34	95	83	135
Balance Defaulted		$ 5	$ 12	$ 11	$ 16
Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		32	71	83	155
Balance Defaulted		$ 2	$ 5	$ 6	$ 11
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		32	49	72	139
Balance Defaulted		$ 1	$ 2	$ 3	$ 6
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	7	18	23	34
Balance Defaulted	[1]	$ 0	$ 1	$ 1	$ 1
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	6	3	7	12
Balance Defaulted	[1]	$ 0	$ 0	$ 0	$ 0
Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		19	26	42	58
Balance Defaulted		$ 0	$ 1	$ 1	$ 1
Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		44	94	109	191
Balance Defaulted		$ 1	$ 1	$ 2	$ 3
Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		100	147	202	313
Balance Defaulted		$ 1	$ 1	$ 1	$ 2
Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		1	3	3	9
Balance Defaulted		$ 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.