ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Recorded Investment in Loan and Leases (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Individually evaluated	$ 1,066	$ 1,114
Formula-based evaluation	118,022	115,546
Total loans and leases	119,088	116,660
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Individually evaluated	399	391
Formula-based evaluation	57,139	56,392
Total loans and leases	57,538	56,783
Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Individually evaluated	667	723
Formula-based evaluation	60,883	59,154
Total loans and leases	$ 61,550	$ 59,877

The balance of financing receivables that were collectively evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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The balance of financing receivables that were individually evaluated for impairment.

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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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