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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	$ 10	$ 11	$ 32	$ 31
Average Recorded Investment	1,000	1,097	926	1,057
Commercial
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	2	3	8	7
Average Recorded Investment	328	368	330	351
Commercial \| Commercial
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	2	3	7	7
Average Recorded Investment	293	334	300	318
Commercial \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	0	0	1	0
Average Recorded Investment	35	34	30	33
Retail
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	8	8	24	24
Average Recorded Investment	672	729	596	706
Retail \| Residential mortgages
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	1	1	4	4
Average Recorded Investment	145	154	128	148
Retail \| Home equity loans
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	1	1	4	4
Average Recorded Investment	94	107	86	107
Retail \| Home equity lines of credit
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	2	2	6	6
Average Recorded Investment	199	202	173	189
Retail \| Home equity loans serviced by others
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	1	1	2	2
Average Recorded Investment	34	43	31	44
Retail \| Home equity lines of credit serviced by others
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	0	0	0	0
Average Recorded Investment	7	9	6	9
Retail \| Automobile
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	1	0	1	0
Average Recorded Investment	21	23	18	21
Retail \| Education
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	2	3	6	7
Average Recorded Investment	141	160	128	159
Retail \| Credit cards
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	0	0	1	1
Average Recorded Investment	26	24	21	22
Retail \| Other retail
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	0	0	0	0
Average Recorded Investment	$ 5	$ 7	$ 5	$ 7

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&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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