DERIVATIVES - Cumulative Basis Adjustments for Fair Value Hedges (Details) - Fair Value Hedging - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Securities due within one year
Derivative [Line Items]
Carrying Amount of the Hedged Item	$ (1,513)	$ (599)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	(15)	0
Long-term debt
Derivative [Line Items]
Carrying Amount of the Hedged Item	0	(1,494)
Cumulative Amount of Fair Value Hedging Adjustment included in Carrying Amount of the Hedged Item	$ 0	$ 3