BORROWED FUNDS - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Principal balance	$ 17,500	$ 16,000
Unamortized deferred issuance costs and/or discounts	77	85
Hedging basis adjustments	(26)	(27)
Short-term borrowed funds	232	3
Available borrowing capacity	61,300
Federal Home Loan Bank Advances and Letters of Credit | Secured Debt
Debt Instrument [Line Items]
Short-term borrowed funds	13,000	15,700
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Available borrowing capacity	$ 12,700	$ 11,500