DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Asset Fair Value
Asset Fair Value	$ 646	$ 640
Less: gross amounts offset in the Consolidated Balance Sheets, Asset Fair Value	0	0
Derivative assets	646	640
Less: amounts subject to master netting agreements, Asset Fair Value	(50)	(97)
Less: cash collateral pledged (received) subject to master netting agreements	(533)	(405)
Total net derivative fair value, Asset Fair Value	63	138
Liability Fair Value
Liability Fair Value	(636)	(636)
Less: gross amounts offset in the Consolidated Balance Sheets, Liability Fair Value	0	0
Derivative liability	(636)	(636)
Less: amounts subject to master netting agreements, Asset Liability Value	50	97
Less: cash collateral pledged (received) subject to master netting agreements	3	39
Total net derivative fair value, Liability Fair Value	(583)	(500)
Variation margin, amount reducing derivative asset	87	66
Variation margin, amount reducing derivative liability	32	37
Qualifying Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	3,999	815
Asset Fair Value
Asset Fair Value	0	0
Liability Fair Value
Liability Fair Value	0	0
Derivative instruments and hedges, assets	2	4
Derivative instruments and hedges, liabilities	2	0
Qualifying Hedges | Fair Value Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	1,499	815
Asset Fair Value
Asset Fair Value	0	0
Liability Fair Value
Liability Fair Value	0	0
Qualifying Hedges | Interest rate contracts | Fair Value Hedges | Time deposits
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	334	0
Asset Fair Value
Asset Fair Value	0	0
Liability Fair Value
Liability Fair Value	0	0
Qualifying Hedges | Interest rate contracts | Fair Value Hedges | Long-term borrowings
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	1,165	815
Asset Fair Value
Asset Fair Value	0	0
Liability Fair Value
Liability Fair Value	0	0
Qualifying Hedges | Interest rate contracts | Cash Flow Hedges | Loans
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	2,500	0
Asset Fair Value
Asset Fair Value	0	0
Liability Fair Value
Liability Fair Value	0	0
Non-qualifying Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	35,184	34,673
Asset Fair Value
Asset Fair Value	646	640
Liability Fair Value
Liability Fair Value	(636)	(636)
Non-qualifying Hedges | Interest rate contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	25,266	24,548
Asset Fair Value
Asset Fair Value	553	530
Liability Fair Value
Liability Fair Value	(569)	(518)
Non-qualifying Hedges | Foreign currency forward contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	8,685	9,142
Asset Fair Value
Asset Fair Value	83	104
Liability Fair Value
Liability Fair Value	(66)	(117)
Non-qualifying Hedges | Foreign exchange spot contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	176	179
Liability Fair Value
Net fair value	0	0
Non-qualifying Hedges | Other contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	1,233	983
Asset Fair Value
Asset Fair Value	10	6
Liability Fair Value
Liability Fair Value	$ (1)	$ (1)