DERIVATIVES ACTIVITIES - Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pretax change in accumulated other comprehensive income (loss)
Total gain (loss) recognized in AOCI	$ (217)	$ 97	$ (545)	$ 139
Other revenue	521	(112)	855	136
Net interest revenue	11,665	11,258	22,837	22,213
Revenue	18,469	18,155	37,341	36,521
Cash flow hedge gain expected to be reclassified from AOCI within 12 months			$ 410
Maximum length of time hedged in cash flow hedge			10 years
Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Total gain (loss) recognized in AOCI	(222)	97	$ (544)	139
Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Total gain (loss) recognized in AOCI	5	0	(1)	0
Cash flow hedges | (Gain) loss reclassified from AOCI
Pretax change in accumulated other comprehensive income (loss)
Other revenue	(6)		(4)
Net interest revenue	(88)		(119)
Revenue		(88)		(47)
Cash flow hedges | (Gain) loss reclassified from AOCI | Interest rate contracts
Pretax change in accumulated other comprehensive income (loss)
Other revenue	0		0
Net interest revenue	(88)		(119)
Revenue		(90)		(46)
Cash flow hedges | (Gain) loss reclassified from AOCI | Foreign exchange contracts
Pretax change in accumulated other comprehensive income (loss)
Other revenue	(6)		(4)
Net interest revenue	$ 0		$ 0
Revenue		$ 2		$ (1)