DERIVATIVES - Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	$ (57)	$ 53	$ (556)	$ (1,568)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	57	(53)	556	1,568
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(40)	32	(58)	(51)
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	454	239	(3,481)	7,086
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(559)	(313)	3,267	(7,128)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	1	(18)	(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	454	239	(3,481)	7,086
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(559)	(313)	3,267	(7,128)
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	1	(18)	(3)	(23)
Foreign exchange contracts (gross)
Gain (loss) on fair value hedges
Amount of cross currency basis included in AOCI	(13)	16	(26)	49
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	220	434	10	(1,477)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	(220)	(434)	(10)	1,477
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	13	17	17	(41)
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	(277)	(381)	(566)	(91)
Gain (loss) on the hedged item in designated and qualifying fair value hedges	277	381	566	91
Net gain (loss) on the hedging derivatives excluded from assessment of the effectiveness of fair value hedges	(53)	15	(75)	(10)
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