BORROWED FUNDS - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Short-term borrowed funds	$ 1,018	$ 3
Hedging basis adjustments	1,679	1,839
Available borrowing capacity	59,400
Federal Home Loan Bank Advances and Letters of Credit | Secured Debt
Debt Instrument [Line Items]
Short-term borrowed funds	18,700	15,700
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Available borrowing capacity	6,800	11,500
Parent Company
Debt Instrument [Line Items]
Principal balance	3,400
Unamortized deferred issuance costs and/or discounts	73	75
Banking Subsidiaries
Debt Instrument [Line Items]
Principal balance	15,500	12,600
Unamortized deferred issuance costs and/or discounts	11	10
Hedging basis adjustments	$ (18)	$ (27)