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, 2016 USD ($) contract	Jun. 30, 2015 USD ($) contract	Jun. 30, 2016 USD ($) contract	Jun. 30, 2015 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		238	283	502	638
Balance Defaulted | $		$ 12	$ 11	$ 26	$ 26
Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		9	8	12	14
Balance Defaulted | $		$ 3	$ 1	$ 3	$ 1
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		8	8	11	14
Balance Defaulted | $		$ 3	$ 1	$ 3	$ 1
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		1	0	1	0
Balance Defaulted | $		$ 0	$ 0	$ 0	$ 0
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		229	275	490	624
Balance Defaulted | $		$ 9	$ 10	$ 23	$ 25
Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		35	34	89	83
Balance Defaulted | $		$ 4	$ 5	$ 12	$ 11
Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		32	32	50	83
Balance Defaulted | $		$ 2	$ 2	$ 3	$ 6
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		20	32	45	72
Balance Defaulted | $		$ 1	$ 1	$ 4	$ 3
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	11	7	21	23
Balance Defaulted | $	[1]	$ 0	$ 0	$ 1	$ 1
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	6	6	11	7
Balance Defaulted | $	[1]	$ 0	$ 0	$ 0	$ 0
Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		22	19	37	42
Balance Defaulted | $		$ 1	$ 0	$ 1	$ 1
Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		18	44	31	109
Balance Defaulted | $		$ 1	$ 1	$ 1	$ 2
Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		85	100	206	202
Balance Defaulted | $		$ 0	$ 1	$ 1	$ 1
Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		0	1	0	3
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.