DERIVATIVES - Cumulative Basis Adjustment (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Debt securities AFS, carrying amount of hedged asset/liability	$ 110,515	$ 81,632
Debt securities AFS, cumulative fair value hedging adjustment included in the carrying amount, active	360	(196)
Debt securities AFS, cumulative fair value hedging adjustment included in the carrying amount, de-designated	628	295
Long-term debt, carrying amount of hedged asset/liability	162,894	149,054
Long-term debt, cumulative fair value hedging adjustment included in the carrying amount, active	4,548	1,211
Long-term debt, cumulative fair value hedging adjustment included in the carrying amount, de-designated	1,407	$ 869
Cumulative basis adjustment associated with hedging relationships	172
Amount of designated hedged items	2,000
Amortized cost basis of closed portfolios used in hedging relations	$ 26,400