DERIVATIVES - Amounts Recorded in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Carrying amount of hedged assets	$ 0	$ 0
Last-of-layer hedging amount	2,000
Carrying value of hedged asset in lay-of-layer hedging relationship	6,000	10,900
Debt securities available for sale
Derivative [Line Items]
Carrying amount of hedged assets	6,042	10,869
Cumulative amount of fair value hedging adjustments included in the carrying amount of the hedged items	29	96
Debt securities available for sale
Derivative [Line Items]
Carrying amount of hedged liabilities	0	0
Long-term borrowed funds
Derivative [Line Items]
Carrying amount of hedged liabilities	2,239	3,307
Cumulative amount of fair value hedging adjustments included in the carrying amount of the hedged items	$ 42	$ 112

Amortized cost of closed portfolio of prepayable financial asset and beneficial interest secured by prepayable financial instrument, used to designate hedging relationship in which hedged item is last layer expected to be remaining at end of hedging relationship.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EEE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999718-113959

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Amount of asset hedged in fair value hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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Amount of asset hedged in last of layer, expected to be remaining at end of hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EEE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999718-113959

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- Definition

Amount of liability hedged in fair value hedging relationship.

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Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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