DERIVATIVE FINANCIAL INSTRUMENTS - Asset and Liability Management (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Notional Disclosures [Abstract]
Notional Value	$ 45,059		$ 44,024
Increase (decrease) to net interest income due to derivative adjustment	(15)	$ (18)
Other long term debt
Notional Disclosures [Abstract]
Notional Value	12,399		10,599
Not Designated as Hedging Instrument, Economic Hedge
Notional Disclosures [Abstract]
Notional Value	28		28
Not Designated as Hedging Instrument, Economic Hedge \| Other long term debt
Notional Disclosures [Abstract]
Notional Value	0		0
Fair Value Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	16,756		15,746
Fair Value Hedges \| Derivatives designated as Hedging Instruments \| Other long term debt
Notional Disclosures [Abstract]
Notional Value	12,399		10,599
Cash Flow Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	28,275		28,250
Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Other long term debt
Notional Disclosures [Abstract]
Notional Value	0		0
Investment securities
Notional Disclosures [Abstract]
Notional Value	4,357		5,147
Investment securities \| Not Designated as Hedging Instrument, Economic Hedge
Notional Disclosures [Abstract]
Notional Value	0		0
Investment securities \| Fair Value Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	4,357		5,147
Investment securities \| Cash Flow Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	0		0
Loans
Notional Disclosures [Abstract]
Notional Value	28,303		28,278
Loans \| Not Designated as Hedging Instrument, Economic Hedge
Notional Disclosures [Abstract]
Notional Value	28		28
Loans \| Fair Value Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	0		0
Loans \| Cash Flow Hedges \| Derivatives designated as Hedging Instruments
Notional Disclosures [Abstract]
Notional Value	$ 28,275		$ 28,250