DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	$ (1,621)	$ 238
Gain (loss) on the hedged item in designated and qualifying fair value hedges	1,621	(238)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(83)	15
Net interest revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	6,847	963
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(6,815)	(879)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(5)	0
Interest rate contracts | Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	0	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	0	0
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	0
Interest rate contracts | Net interest revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	6,847	963
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(6,815)	(879)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(5)	0
Foreign exchange contracts
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	33	24
Foreign exchange contracts | Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	(1,911)	168
Gain (loss) on the hedged item in designated and qualifying fair value hedges	1,911	(168)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(58)	(3)
Foreign exchange contracts | Net interest revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	0	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	0	0
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	0
Commodity and other contracts | Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	290	70
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(290)	(70)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(25)	18
Commodity and other contracts | Net interest revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	0	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	0	0
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	$ 0	$ 0