LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing receivable impaired
Carrying Value	$ 41	$ 236	$ 44	$ 307
Period within which default occurred post-modification			1 year
Number of days past due, default status			60 days
Carrying Value	598	855	$ 598	855
TDR in payment default	11	3	70	15
Commercial and industrial
Financing receivable impaired
Carrying Value	39	233	41	288
Carrying Value	440	591	440	591
TDR in payment default	11	3	70	12
Financial institutions
Financing receivable impaired
Carrying Value	34	24	34	24
TDR in payment default	0	0	0	3
Mortgage and real estate
Financing receivable impaired
Carrying Value	2	3	3	15
Carrying Value	87	74	87	74
TDR in payment default	0	0	0	0
Other
Financing receivable impaired
Carrying Value				4
Carrying Value	37	166	37	166
TDR 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	3	32	$ 3	32
TDRs involving changes in the amount and/or timing of principal payments \| Commercial and industrial
Financing receivable impaired
Carrying Value	3	32	3	32
TDRs involving changes in the amount and/or timing of principal payments \| Mortgage and real estate
Financing receivable impaired
Carrying Value	0	0	0	0
TDRs involving changes in the amount and/or timing of principal payments \| Other
Financing receivable impaired
Carrying Value				0
TDRs involving changes in the amount and/or timing of interest payments
Financing receivable impaired
Carrying Value	4	0	4	0
TDRs involving changes in the amount and/or timing of interest payments \| Commercial and industrial
Financing receivable impaired
Carrying Value	4	0	4	0
TDRs involving changes in the amount and/or timing of interest payments \| Mortgage and real estate
Financing receivable impaired
Carrying Value	0	0	0	0
TDRs involving changes in the amount and/or timing of interest payments \| Other
Financing receivable impaired
Carrying Value				0
TDRs involving changes in the amount and/or timing of both principal and interest payments
Financing receivable impaired
Carrying Value	34	204	37	275
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Commercial and industrial
Financing receivable impaired
Carrying Value	32	201	34	256
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Mortgage and real estate
Financing receivable impaired
Carrying Value	$ 2	$ 3	$ 3	15
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Other
Financing receivable impaired
Carrying Value				$ 4

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

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- Definition

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

+ References

No definition available.

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- Definition

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+ References

No definition available.

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- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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