LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing receivable impaired
Carrying value of TDRs modified during the period	$ 57	$ 94	$ 80	$ 160
Period within which default occurred post-modification			1 year
Number of days past due, default status			60 days
TDR balance	416	507	$ 416	507
TDR loans in payment default	0	0	0	0
Commercial and industrial
Financing receivable impaired
Carrying value of TDRs modified during the period	52	86	73	148
TDR balance	298	406	298	406
TDR loans in payment default	0	0	0	0
Mortgage and real estate
Financing receivable impaired
Carrying value of TDRs modified during the period	5	4	6	8
TDR balance	80	91	80	91
TDR loans in payment default	0	0	0	0
Other
Financing receivable impaired
Carrying value of TDRs modified during the period	0	4	1	4
TDR balance	38	10	38	10
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	0	4	$ 1	4
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	0	0	0	0
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	0	4	1	4
TDRs involving changes in the amount and/or timing of interest payments
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 \| Commercial and industrial
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 \| 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	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	57	90	79	156
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	52	86	73	148
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	5	4	6	8
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	$ 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

No definition available.

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- Definition

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- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

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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=123577603&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=121585226&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=123577603&loc=SL6953682-111524

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