LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Financing receivable impaired
Carrying Value	$ 3	$ 71
Period within which default occurred post-modification	1 year
Number of days past due, default status	60 days
Carrying Value	$ 686	675
TDR in payment default	59	12
Commercial and industrial
Financing receivable impaired
Carrying Value	2	55
Carrying Value	507	390
TDR in payment default	59	9
Financial institutions
Financing receivable impaired
Carrying Value		15
Carrying Value	40	24
TDR in payment default	0	3
Mortgage and real estate
Financing receivable impaired
Carrying Value	1	1
Carrying Value	98	84
TDR in payment default	0	0
Other
Financing receivable impaired
Carrying Value	41	177
TDR in payment default	$ 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	$ 0	0
TDRs involving changes in the amount and/or timing of principal payments \| Commercial and industrial
Financing receivable impaired
Carrying Value	0	0
TDRs involving changes in the amount and/or timing of principal payments \| Financial institutions
Financing receivable impaired
Carrying Value		0
TDRs involving changes in the amount and/or timing of principal payments \| Mortgage and real estate
Financing receivable impaired
Carrying Value	0	0
TDRs involving changes in the amount and/or timing of interest payments
Financing receivable impaired
Carrying Value	0	0
TDRs involving changes in the amount and/or timing of interest payments \| Commercial and industrial
Financing receivable impaired
Carrying Value	0	0
TDRs involving changes in the amount and/or timing of interest payments \| Financial institutions
Financing receivable impaired
Carrying Value		0
TDRs involving changes in the amount and/or timing of interest payments \| Mortgage and real estate
Financing receivable impaired
Carrying Value	0	0
TDRs involving changes in the amount and/or timing of both principal and interest payments
Financing receivable impaired
Carrying Value	3	71
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Commercial and industrial
Financing receivable impaired
Carrying Value	2	55
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Financial institutions
Financing receivable impaired
Carrying Value		15
TDRs involving changes in the amount and/or timing of both principal and interest payments \| Mortgage and real estate
Financing receivable impaired
Carrying Value	$ 1	$ 1

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://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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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