ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Additional Impaired Loan Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	$ 35	$ 47	$ 53
Average Recorded Investment	1,102	1,283	1,434
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	5	5	11
Average Recorded Investment	351	179	296
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	5	4	9
Average Recorded Investment	295	135	198
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	1	2
Average Recorded Investment	53	44	98
Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0
Average Recorded Investment	3	0	0
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	30	42	42
Average Recorded Investment	751	1,104	1,138
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	4	15	14
Average Recorded Investment	161	415	429
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	7	9	8
Average Recorded Investment	144	222	246
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	6	4	4
Average Recorded Investment	178	173	149
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	3	4	5
Average Recorded Investment	60	75	91
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0
Average Recorded Investment	9	9	11
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0
Average Recorded Investment	14	11	7
Student
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	7	7	8
Average Recorded Investment	150	157	153
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	2	2	2
Average Recorded Investment	23	26	31
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	1	1
Average Recorded Investment	$ 12	$ 16	$ 21

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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