ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Additional Impaired Loan Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	$ 11	$ 10
Average Recorded Investment	1,014	1,065
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	3	2
Average Recorded Investment	327	320
Commercial \| Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	3	2
Average Recorded Investment	301	293
Commercial \| Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0
Average Recorded Investment	26	27
Commercial \| Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0
Average Recorded Investment	0	0
Retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	8	8
Average Recorded Investment	687	745
Retail \| Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	1
Average Recorded Investment	143	149
Retail \| Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	2	2
Average Recorded Investment	101	118
Retail \| Home equity lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	2	2
Average Recorded Investment	196	194
Retail \| Home equity loans serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	1	1
Average Recorded Investment	39	50
Retail \| Home equity lines of credit serviced by others
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0
Average Recorded Investment	7	9
Retail \| Automobile
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0
Average Recorded Investment	21	22
Retail \| Education
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	2	2
Average Recorded Investment	150	171
Retail \| Credit cards
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0
Average Recorded Investment	24	24
Retail \| Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest Income Recognized	0	0
Average Recorded Investment	$ 6	$ 8

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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=84173941&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=84173941&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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