BORROWED FUNDS - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Principal balance	$ 12,400	$ 12,500
Unamortized deferred issuance costs and/or discounts	84	85
Hedging basis adjustments	(6)	(8)
Short-term borrowed funds	47	0
Available borrowing capacity	77,400
Federal Home Loan Bank Advances and Letters of Credit | Secured Debt
Debt Instrument [Line Items]
Short-term borrowed funds	4,700	4,600
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Available borrowing capacity	$ 23,000	$ 21,100