DERIVATIVES - Amounts Recorded in Balance Sheet (Details) $ in Millions	Dec. 31, 2019 USD ($)
Debt securities available for sale
Derivative [Line Items]
Carrying amount of hedged assets	$ 15,798
Cumulative amount of fair value hedging adjustments included in the carrying amount of the hedged items	(8)
Last-of-layer hedging amount	2,000
Carrying value of hedged asset in lay-of-layer hedging relationship	15,800
Residential mortgages
Derivative [Line Items]
Carrying amount of hedged assets	976
Cumulative amount of fair value hedging adjustments included in the carrying amount of the hedged items	17
Long-term borrowed funds
Derivative [Line Items]
Carrying amount of hedged assets	0
Debt securities available for sale
Derivative [Line Items]
Carrying amount of hedged liabilities	0
Residential mortgages
Derivative [Line Items]
Carrying amount of hedged liabilities	0
Long-term borrowed funds
Derivative [Line Items]
Carrying amount of hedged liabilities	4,689
Cumulative amount of fair value hedging adjustments included in the carrying amount of the hedged items	$ 50

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=109980867&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=109980867&loc=SL109999712-113959

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+ 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=109980867&loc=SL109999712-113959

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+ 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=109980867&loc=SL109999718-113959

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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
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-SubTopic 10
-Section 50
-Paragraph 4EE
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