LOANS AND LEASES - Summary of Payment Status of TDRs (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled debt restructurings ("TDRs")	$ 93	$ 91
Performing [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled debt restructurings ("TDRs")	58	58
Non-Accrual [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Troubled debt restructurings ("TDRs")	$ 35	$ 33

Amount of financing receivable modified as troubled debt restructuring.

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

Reference 2: 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=121585226&loc=d3e18845-111554

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant