ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Additional Impaired Loan Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		$ 11	$ 13	$ 35	$ 35
Average Recorded Investment		1,320	1,396	1,310	1,368
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		1	2	3	3
Average Recorded Investment		161	200	178	211
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		1	2	2	2
Average Recorded Investment		126	138	133	141
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		0	0	1	1
Average Recorded Investment		35	62	45	70
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		10	11	32	32
Average Recorded Investment		1,159	1,196	1,132	1,157
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		4	4	12	11
Average Recorded Investment		428	445	423	434
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		2	1	7	5
Average Recorded Investment		277	262	263	248
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		1	1	3	3
Average Recorded Investment		142	158	140	153
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	[1]	1	1	3	4
Average Recorded Investment	[1]	79	95	80	94
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	[1]	0	0	0	0
Average Recorded Investment	[1]	10	11	9	11
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		0	0	0	0
Average Recorded Investment		12	9	11	8
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		1	2	5	6
Average Recorded Investment		165	161	160	154
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		0	1	1	2
Average Recorded Investment		29	34	28	34
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized		1	1	1	1
Average Recorded Investment		$ 17	$ 21	$ 18	$ 21

[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.