DERIVATIVE FINANCIAL INSTRUMENTS - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025
Derivative Instruments, Gain (Loss) [Line Items]
Cumulative Amount of Fair Value Hedging Adjustment To Hedged Items	$ 196		$ 177
Fair value hedging adjustments	(39)		(42)
Investment Securities
Derivative Instruments, Gain (Loss) [Line Items]
Designated hedged items	4,400
Subordinated notes | Other long term debt
Derivative Instruments, Gain (Loss) [Line Items]
Liabilities, Amortized Cost	12,249		11,066
Cumulative Amount of Fair Value Hedging Adjustment To Hedged Items	(69)		1
Interest rate contracts | Investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Assets, Amortized Cost	16,000		11,402
Cumulative Amount of Fair Value Hedging Adjustment To Hedged Items	(196)		$ (177)
Interest income available for sale securities taxable | Investment Securities
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value for derivatives designated as fair value hedges	22	$ (122)
Interest income available for sale securities taxable | Hedged investment securities
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value for derivatives designated as fair value hedges	(18)	123
Interest expense subordinated notes and other long term debt | Subordinated notes
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value for derivatives designated as fair value hedges	(70)	143
Interest expense subordinated notes and other long term debt | Hedged Subordinated notes
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value for derivatives designated as fair value hedges	$ 71	$ (143)