DERIVATIVES - Cumulative Basis Adjustment (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Debt securities AFS, carrying amount of hedged asset/liability	$ 99,152	$ 94,659
Debt securities AFS, cumulative fair value hedging adjustment included in the carrying amount, active	22	(114)
Debt securities AFS, cumulative fair value hedging adjustment included in the carrying amount, de-designated	385	743
Long-term debt, carrying amount of hedged asset/liability	170,069	157,387
Long-term debt, cumulative fair value hedging adjustment included in the carrying amount, active	7,811	2,334
Long-term debt, cumulative fair value hedging adjustment included in the carrying amount, de-designated	4,197	3,445
Cumulative basis adjustment within active hedges	7	(8)
Cumulative basis adjustment within de-designated hedges	74	157
Amount of designated hedged items	1,768	605
Amortized cost basis of closed portfolios used in hedging relations	$ 20,000	$ 20,000