BORROWED FUNDS - Short Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 4,359	$ 3,432
Federal funds purchased
Short-term Debt [Line Items]
Total short-term borrowed funds	533	0
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Total short-term borrowed funds	615	802
Other short-term borrowed funds (primarily current portion of FHLB advances)
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 3,211	$ 2,630