ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Additional Impaired Loan Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	$ 9	$ 10	$ 18	$ 18
Average Recorded Investment	1,259	1,175	1,231	1,090
Commercial Banking
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	2	2	3
Average Recorded Investment	469	382	455	309
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	2	2	3
Average Recorded Investment	431	324	414	248
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0	0
Average Recorded Investment	38	58	41	61
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	8	8	16	15
Average Recorded Investment	790	793	776	781
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	2	1	3	2
Average Recorded Investment	182	160	178	156
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	1	3	3
Average Recorded Investment	141	158	140	154
Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	2	3	3
Average Recorded Investment	203	184	197	182
Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	1	2	2
Average Recorded Investment	54	66	54	67
Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0	0
Average Recorded Investment	9	10	9	9
Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0	0
Average Recorded Investment	20	15	18	14
Education
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	2	2	4	4
Average Recorded Investment	146	161	146	160
Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	1	1	1
Average Recorded Investment	25	26	24	26
Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0	0	0
Average Recorded Investment	$ 10	$ 13	$ 10	$ 13

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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.

+ References

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