LOANS - Corporate Troubled Debt Restructurings (Details) - Corporate - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing receivable impaired
Carrying value of TDRs modified during the period	$ 7	$ 61	$ 87	$ 221
Period within which default occurred post-modification			1 year
Number of days past due, default status			60 days
TDR balance	368	510	$ 368	510
TDR loans in payment default	0	0	0	0
Commercial and industrial
Financing receivable impaired
Carrying value of TDRs modified during the period	2	52	75	200
TDR balance	252	390	252	390
TDR loans in payment default	0	0	0	0
Mortgage and real estate
Financing receivable impaired
Carrying value of TDRs modified during the period	1	8	7	16
TDR balance	65	98	65	98
TDR loans in payment default	0	0	0	0
Other
Financing receivable impaired
Carrying value of TDRs modified during the period	4	1	5	5
TDR balance	51	22	51	22
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	1	$ 1	5
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	1	1	5
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	7	60	86	216
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	2	52	75	200
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	1	8	7	16
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	$ 4	$ 0	$ 4	$ 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=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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