DERIVATIVE FINANCIAL INSTRUMENTS - Asset and Liability Management (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Notional Disclosures [Abstract]
Notional Value	$ 111,887		$ 111,887		$ 103,047
Increase (decrease) to net interest income due to derivative adjustment	(18)	$ (7)	(33)	$ (25)
Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	43,624		43,624		44,024
Other long term debt \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	12,399		12,399		10,599
Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	43,596		43,596		43,996
Not Designated as Hedging Instrument, Economic Hedge \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	28		28		28
Not Designated as Hedging Instrument, Economic Hedge \| Other long term debt \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	0		0		0
Fair Value Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	18,021		18,021		15,746
Fair Value Hedges \| Derivatives designated as Hedging Instruments \| Other long term debt \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	12,399		12,399		10,599
Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	25,575		25,575		28,250
Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Other long term debt \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	0		0		0
Investment securities \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	5,622		5,622		5,147
Investment securities \| Not Designated as Hedging Instrument, Economic Hedge \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	0		0		0
Investment securities \| Fair Value Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	5,622		5,622		5,147
Investment securities \| Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	0		0		0
Loans \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	25,603		25,603		28,278
Loans \| Not Designated as Hedging Instrument, Economic Hedge \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	28		28		28
Loans \| Fair Value Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	0		0		0
Loans \| Cash Flow Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	25,600		25,600
Loans \| Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	$ 25,575		$ 25,575		$ 28,250