BORROWED FUNDS - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Principal balance	$ 13,600	$ 16,000
Unamortized deferred issuance costs and or discounts	74	85
Cumulative amount of fair value hedging adjustments included in the carrying amount of the hedged items	(17)	(27)
Short-term borrowed funds	505	3
Available borrowing capacity	69,000
FHLB advances and letters of credit | Secured Debt
Debt Instrument [Line Items]
Short-term borrowed funds	9,200	15,700
Pledged as collateral for FHLB borrowing capacity
Debt Instrument [Line Items]
Available borrowing capacity	$ 15,900	$ 11,500