BORROWED FUNDS - Short Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 3,432	$ 10,529
Federal funds purchased
Short-term Debt [Line Items]
Total short-term borrowed funds	0	574
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Total short-term borrowed funds	802	3,702
Other short-term borrowed funds (primarily current portion of FHLB advances)
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 2,630	$ 6,253