ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Default of Modified Debt Agreements (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($) contract	Sep. 30, 2015 USD ($) contract	Sep. 30, 2014 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		298	532	936	1,596
Balance Defaulted		$ 21	$ 29	$ 47	$ 73
Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		7	6	21	24
Balance Defaulted		$ 1	$ 4	$ 2	$ 8
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		7	5	21	22
Balance Defaulted		$ 1	$ 4	$ 2	$ 7
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		0	1	0	2
Balance Defaulted		$ 0	$ 0	$ 0	$ 1
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		291	526	915	1,572
Balance Defaulted		$ 20	$ 25	$ 45	$ 65
Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		37	91	120	226
Balance Defaulted		$ 7	$ 11	$ 18	$ 27
Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		47	104	130	259
Balance Defaulted		$ 6	$ 8	$ 12	$ 19
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		26	52	98	191
Balance Defaulted		$ 3	$ 3	$ 6	$ 9
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	11	17	34	51
Balance Defaulted	[1]	$ 1	$ 0	$ 2	$ 1
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	10	6	17	18
Balance Defaulted	[1]	$ 1	$ 0	$ 1	$ 0
Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		24	30	66	88
Balance Defaulted		$ 0	$ 0	$ 1	$ 1
Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		33	93	142	284
Balance Defaulted		$ 1	$ 2	$ 3	$ 5
Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		102	131	304	444
Balance Defaulted		$ 1	$ 1	$ 2	$ 3
Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		1	2	4	11
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.