DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ (352)	$ 322	$ (114)	$ 499
Gain (loss) on the hedged item in designated and qualifying fair value hedges	352	(347)	114	(595)
Net gain (loss), on the hedging derivatives, excluded from assessment of the effectiveness of fair value hedges	(113)	34	(98)	58
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	1,853	(518)	2,816	360
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(1,783)	520	(2,662)	(346)
Net gain (loss), on the hedging derivatives, excluded from assessment of the effectiveness of fair value hedges	(4)	(5)	(4)	(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	1,853	(518)	2,816	360
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(1,783)	520	(2,662)	(346)
Net gain (loss), on the hedging derivatives, excluded from assessment of the effectiveness of fair value hedges	(4)	(5)	(4)	(5)
Foreign exchange contracts
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	59	(37)	83	(42)
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	(180)	320	(12)	499
Gain (loss) on the hedged item in designated and qualifying fair value hedges	180	(347)	12	(596)
Net gain (loss), on the hedging derivatives, excluded from assessment of the effectiveness of fair value hedges	(118)	33	(121)	56
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	(172)	2	(102)	0
Gain (loss) on the hedged item in designated and qualifying fair value hedges	172	0	102	1
Net gain (loss), on the hedging derivatives, excluded from assessment of the effectiveness of fair value hedges	5	1	23	2
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