LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing receivable impaired
Carrying value of TDRs modified during the period	$ 51	$ 41	$ 71	$ 44
Period within which default occurred post-modification			1 year
Number of days past due, default status			60 days
TDR balance	552	598	$ 552	598
TDR loans in payment default	19	11	19	70
Commercial and industrial
Financing receivable impaired
Carrying value of TDRs modified during the period	42	39	58	41
TDR balance	424	440	424	440
TDR loans in payment default	19	11	19	70
Financial institutions
Financing receivable impaired
TDR balance	10	34	10	34
TDR loans in payment default	0	0	0	0
Mortgage and real estate
Financing receivable impaired
Carrying value of TDRs modified during the period	3	2	7	3
TDR balance	112	87	112	87
TDR loans in payment default	0	0	0	0
Other
Financing receivable impaired
Carrying value of TDRs modified during the period	6		6
TDR balance	6	37	6	37
TDR loans in payment default	0	0	$ 0	0
Commercial banking loans
Financing receivable impaired
Number of days past due, default status			90 days
TDRs involving changes in the amount and/or timing of principal payments
Financing receivable impaired
Carrying value of TDRs modified during the period	25	3	$ 25	3
TDRs involving changes in the amount and/or timing of principal payments \| Commercial and industrial
Financing receivable impaired
Carrying value of TDRs modified during the period	19	3	19	3
TDRs involving changes in the amount and/or timing of principal payments \| Mortgage and real estate
Financing receivable impaired
Carrying value of TDRs modified during the period	0	0	0	0
TDRs involving changes in the amount and/or timing of principal payments \| Other
Financing receivable impaired
Carrying value of TDRs modified during the period	6		6
TDRs involving changes in the amount and/or timing of interest payments
Financing receivable impaired
Carrying value of TDRs modified during the period	0	4	0	4
TDRs involving changes in the amount and/or timing of interest payments \| Commercial and industrial
Financing receivable impaired
Carrying value of TDRs modified during the period	0	4	0	4
TDRs involving changes in the amount and/or timing of interest payments \| Mortgage and real estate
Financing receivable impaired
Carrying value of TDRs modified during the period	0	0	0	0
TDRs involving changes in the amount and/or timing of interest payments \| Other
Financing receivable impaired
Carrying value of TDRs modified during the period	0		0
TDRs involving changes in the amount and/or timing of both principal and interest payments
Financing receivable impaired
Carrying value of TDRs modified during the period	26	34	46	37
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Commercial and industrial
Financing receivable impaired
Carrying value of TDRs modified during the period	23	32	39	34
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Mortgage and real estate
Financing receivable impaired
Carrying value of TDRs modified during the period	3	$ 2	7	$ 3
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Other
Financing receivable impaired
Carrying value of TDRs modified during the period	$ 0		$ 0

This represents the period within which the payment default occurred after the loan modification.

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Represents the classified default number of days for which the loan is past due.

+ References

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- Definition

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- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

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-Publisher FASB
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-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554

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- Definition

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

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