DERIVATIVE FINANCIAL INSTRUMENTS - Asset and Liability Management (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Notional Disclosures [Abstract]
Notional Value	$ 109,612		$ 109,612		$ 103,047
Increase (decrease) to net interest income due to derivative adjustment	(21)	$ (38)	(54)	$ (63)
Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	41,874		41,874		44,024
Other long term debt \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	11,399		11,399		10,599
Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	41,846		41,846		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	17,021		17,021		15,746
Fair Value Hedges \| Derivatives designated as Hedging Instruments \| Other long term debt \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	11,399		11,399		10,599
Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	24,825		24,825		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	24,853		24,853		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	24,800		24,800
Loans \| Cash Flow Hedges \| Derivatives designated as Hedging Instruments \| Interest rate contracts
Notional Disclosures [Abstract]
Notional Value	$ 24,825		$ 24,825		$ 28,250