BORROWED FUNDS - Short Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 4,014	$ 3,432
Federal funds purchased
Short-term Debt [Line Items]
Total short-term borrowed funds	23	0
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Total short-term borrowed funds	691	802
Other short-term borrowed funds (primarily current portion of FHLB advances)
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 3,300	$ 2,630