ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Default of Modified Debt Agreements (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015 USD ($) contract	Dec. 31, 2014 USD ($) contract	Dec. 31, 2013 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		1,288	2,037	3,584
Balance Defaulted | $		$ 52	$ 97	$ 153
Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		23	40	21
Balance Defaulted | $		$ 2	$ 13	$ 2
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		23	37	18
Balance Defaulted | $		$ 2	$ 12	$ 1
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		0	3	3
Balance Defaulted | $		$ 0	$ 1	$ 1
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		1,265	1,997	3,563
Balance Defaulted | $		$ 50	$ 84	$ 151
Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		168	301	526
Balance Defaulted | $		$ 21	$ 35	$ 60
Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		184	329	740
Balance Defaulted | $		$ 13	$ 24	$ 43
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		131	229	394
Balance Defaulted | $		$ 7	$ 12	$ 21
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	43	60	187
Balance Defaulted | $	[1]	$ 1	$ 2	$ 3
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract	[1]	22	20	42
Balance Defaulted | $	[1]	$ 1	$ 0	$ 2
Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		87	112	208
Balance Defaulted | $		$ 1	$ 1	$ 1
Student
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		171	355	885
Balance Defaulted | $		$ 3	$ 7	$ 17
Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		455	579	548
Balance Defaulted | $		$ 3	$ 3	$ 3
Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts | contract		4	12	33
Balance Defaulted | $		$ 0	$ 0	$ 1

[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.