DERIVATIVES ACTIVITIES - Cumulative Basis Adjustment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Debt securities AFS, carrying amount of hedged asset/liability	$ 98,902	$ 81,632
Debt securities AFS, cumulative fair value hedging adjustment included in the carrying amount, active	302	(196)
Debt securities AFS, cumulative fair value hedging adjustment included in the carrying amount, de-designated	329	295
Long-term debt, carrying amount of hedged asset/liability	157,139	149,054
Long-term debt, cumulative fair value hedging adjustment included in the carrying amount, active	2,275	1,211
Long-term debt, cumulative fair value hedging adjustment included in the carrying amount, de-designated	1,236	$ 869
Cumulative basis adjustment associated with hedging relationships	46
Amount of designated hedged items	2,000
Amortized cost basis of closed portfolios used in hedging relations	$ 16,500