DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	$ (499)	$ (1,621)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	499	1,621
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(18)	(83)
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	(3,935)	6,847
Gain (loss) on the hedged item in designated and qualifying fair value hedges	3,826	(6,815)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(4)	(5)
Interest rate contracts (gross) | 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 (gross) | 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	(3,935)	6,847
Gain (loss) on the hedged item in designated and qualifying fair value hedges	3,826	(6,815)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(4)	(5)
Foreign exchange contracts (gross)
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	(13)	33
Foreign exchange contracts (gross) | Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	(210)	(1,911)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	210	1,911
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	4	(58)
Foreign exchange contracts (gross) | 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 hedges | Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	(289)	290
Gain (loss) on the hedged item in designated and qualifying fair value hedges	289	(290)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(22)	(25)
Commodity hedges | 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