ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Impaired Loans by Class (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		$ 641	$ 789
Allowance on Impaired Loans		137	129
Impaired Loans Without a Related Allowance		742	624
Unpaid Contractual Balance		1,671	1,727
Total Recorded Investment in Impaired Loans		1,383	1,413
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		148	131
Allowance on Impaired Loans		36	20
Impaired Loans Without a Related Allowance		70	74
Unpaid Contractual Balance		214	240
Total Recorded Investment in Impaired Loans		218	205
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		92	124
Allowance on Impaired Loans		23	19
Impaired Loans Without a Related Allowance		58	36
Unpaid Contractual Balance		144	178
Total Recorded Investment in Impaired Loans		150	160
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		56	7
Allowance on Impaired Loans		13	1
Impaired Loans Without a Related Allowance		12	38
Unpaid Contractual Balance		70	62
Total Recorded Investment in Impaired Loans		68	45
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		493	658
Allowance on Impaired Loans		101	109
Impaired Loans Without a Related Allowance		672	550
Unpaid Contractual Balance		1,457	1,487
Total Recorded Investment in Impaired Loans		1,165	1,208
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		121	157
Allowance on Impaired Loans		16	18
Impaired Loans Without a Related Allowance		320	288
Unpaid Contractual Balance		608	605
Total Recorded Investment in Impaired Loans		441	445
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		85	129
Allowance on Impaired Loans		11	11
Impaired Loans Without a Related Allowance		139	141
Unpaid Contractual Balance		283	335
Total Recorded Investment in Impaired Loans		224	270
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		27	75
Allowance on Impaired Loans		2	3
Impaired Loans Without a Related Allowance		167	86
Unpaid Contractual Balance		234	193
Total Recorded Investment in Impaired Loans		194	161
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance	[1]	50	75
Allowance on Impaired Loans	[1]	8	9
Impaired Loans Without a Related Allowance	[1]	24	16
Unpaid Contractual Balance	[1]	88	102
Total Recorded Investment in Impaired Loans	[1]	74	91
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance	[1]	3	4
Allowance on Impaired Loans	[1]	1	1
Impaired Loans Without a Related Allowance	[1]	7	7
Unpaid Contractual Balance	[1]	14	14
Total Recorded Investment in Impaired Loans	[1]	10	11
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		3	2
Allowance on Impaired Loans		0	1
Impaired Loans Without a Related Allowance		11	9
Unpaid Contractual Balance		19	16
Total Recorded Investment in Impaired Loans		14	11
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		163	167
Allowance on Impaired Loans		48	48
Impaired Loans Without a Related Allowance		2	0
Unpaid Contractual Balance		165	167
Total Recorded Investment in Impaired Loans		165	167
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		28	32
Allowance on Impaired Loans		11	13
Impaired Loans Without a Related Allowance		0	0
Unpaid Contractual Balance		28	32
Total Recorded Investment in Impaired Loans		28	32
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired Loans With a Related Allowance		13	17
Allowance on Impaired Loans		4	5
Impaired Loans Without a Related Allowance		2	3
Unpaid Contractual Balance		18	23
Total Recorded Investment in Impaired Loans		$ 15	$ 20

[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.