DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 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	$ 1,232	$ (1,120)	$ (336)	$ (1,234)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(1,232)	1,240	336	1,234
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	67	36	16	(62)
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	(1,121)	1,363	5,965	4,179
Gain (loss) on the hedged item in designated and qualifying fair value hedges	955	(1,320)	(6,173)	(3,982)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	(4)	(23)	(8)
Interest rate 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	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 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	(1,121)	1,363	5,965	4,179
Gain (loss) on the hedged item in designated and qualifying fair value hedges	955	(1,320)	(6,173)	(3,982)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	0	(4)	(23)	(8)
Foreign exchange hedges
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	(51)	(10)	(2)	73
Foreign exchange 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	1,235	(1,180)	(242)	(1,192)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(1,235)	1,180	242	1,192
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(24)	25	(65)	(96)
Foreign exchange 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
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	(3)	60	(94)	(42)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	3	60	94	42
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	91	11	81	34
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