DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other revenue
Gain (loss) on fair value hedges
Gain (loss) on the hedging derivatives included in assessment of the effectiveness of fair value hedges	$ (1,120)	$ (149)	$ (1,234)	$ (1,510)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	1,120	150	1,234	1,511
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	36	(14)	(62)	(9)
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	1,363	(857)	4,179	(497)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(1,320)	871	(3,982)	525
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(4)	0	(8)	(5)
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	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 | 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	1,363	(857)	4,179	(497)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(1,320)	871	(3,982)	525
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(4)	0	(8)	(5)
Foreign exchange contracts
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	(10)	13	73	(29)
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	(1,180)	(142)	(1,192)	(1,502)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	1,180	142	1,192	1,502
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	25	(7)	(96)	(2)
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	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 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	60	(7)	(42)	(8)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(60)	8	42	9
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	11	(7)	34	(7)
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	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