DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Asset Fair Value
Asset Fair Value	$ 626	$ 660
Less: gross amounts offset in the Consolidated Balance Sheets, Asset Fair Value	0	0
Derivative assets	626	660
Liability Fair Value
Liability Fair Value	(631)	(625)
Less: gross amounts offset in the Consolidated Balance Sheets, Liability Fair Value	0	0
Derivative liability	(631)	(625)
Qualifying Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	3,334	4,584
Asset Fair Value
Asset Fair Value	0	1
Liability Fair Value
Liability Fair Value	0	0
Qualifying Hedges | Fair Value Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	334	1,084
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	134	334
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	200	750
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	3,000	3,500
Asset Fair Value
Asset Fair Value	0	1
Liability Fair Value
Liability Fair Value	0	0
Non-qualifying Hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	37,649	35,394
Asset Fair Value
Asset Fair Value	626	659
Liability Fair Value
Liability Fair Value	(631)	(625)
Non-qualifying Hedges | Interest rate contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	27,721	26,235
Asset Fair Value
Asset Fair Value	418	491
Liability Fair Value
Liability Fair Value	(411)	(516)
Non-qualifying Hedges | Foreign exchange contract
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	8,408	7,843
Asset Fair Value
Asset Fair Value	188	152
Liability Fair Value
Liability Fair Value	(219)	(108)
Non-qualifying Hedges | Foreign exchange spot contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	300	177
Liability Fair Value
Net fair value	0	0
Non-qualifying Hedges | Other contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amount	1,520	1,316
Asset Fair Value
Asset Fair Value	20	16
Liability Fair Value
Liability Fair Value	$ (1)	$ (1)