BORROWED FUNDS - Short Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 3,855	$ 4,359
Federal funds purchased
Short-term Debt [Line Items]
Total short-term borrowed funds	566	533
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Total short-term borrowed funds	527	615
Other short-term borrowed funds (primarily current portion of FHLB advances)
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 2,762	$ 3,211