DERIVATIVES - Schedule of Gains (Losses) on All Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Cross-currency swaps \| Fair value hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	$ 0	$ 0	$ 0	$ (1)
Interest rate swaps \| Fair value hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	(97)	7	(90)	18
Pay fixed-receive variable interest rate swaps \| Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	2	6	8	18
Pay variable receive-fixed interest rate swap \| Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	(3)	(38)	(17)	(110)
Mortgage banking derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	(6)	0	(9)	3
Customer-related derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	165	(3)	172	80
Foreign exchange
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	51	33	103	(57)
Interest rate swaps, caps, and options
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	0	0	0	(1)
Other
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized on derivatives	$ 765	$ (90)	$ 837	$ (287)