DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 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	$ (890)	$ 1,232	$ (1,446)	$ (336)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	891	(1,232)	1,447	336
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	121	67	63	16
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	(747)	(1,121)	(4,228)	5,965
Gain (loss) on the hedged item in designated and qualifying fair value hedges	667	955	3,934	(6,173)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	0	(3)	(23)
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	0	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	0	0	0	0
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	0	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	(747)	(1,121)	(4,228)	5,965
Gain (loss) on the hedged item in designated and qualifying fair value hedges	667	955	3,934	(6,173)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	0	(3)	(23)
Foreign exchange contracts (gross)
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	12	(51)	(14)	(2)
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	(724)	1,235	(714)	(242)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	725	(1,235)	715	242
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	79	(24)	96	(65)
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	0	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	0	0	0	0
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	0	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	(166)	(3)	(732)	(94)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	166	3	732	94
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	42	91	(33)	81
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	0	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	0	0	0	0
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	$ 0	$ 0	$ 0	$ 0