BORROWED FUNDS - Short Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 3,412	$ 3,432
Federal funds purchased
Short-term Debt [Line Items]
Total short-term borrowed funds	95	0
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Total short-term borrowed funds	805	802
Other short-term borrowed funds (primarily current portion of FHLB advances)
Short-term Debt [Line Items]
Total short-term borrowed funds	$ 2,512	$ 2,630