PRINCIPAL TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Principal transactions revenue
Principal transactions revenue	$ 2,151	$ 2,643	$ 5,440	$ 5,737
Interest rate risks
Principal transactions revenue
Principal transactions revenue	1,551	1,495	3,173	3,241
Foreign exchange risks
Principal transactions revenue
Principal transactions revenue	175	757	920	1,336
Equity risks
Principal transactions revenue
Principal transactions revenue	120	74	686	286
Commodity and other risks
Principal transactions revenue
Principal transactions revenue	208	169	300	322
Credit products and risks
Principal transactions revenue
Principal transactions revenue	97	148	361	552
Citicorp
Principal transactions revenue
Principal transactions revenue	2,151	2,643	5,440	5,737
Global Consumer Banking | Operating Segments
Principal transactions revenue
Principal transactions revenue	143	152	293	307
Institutional Clients Group | Operating Segments
Principal transactions revenue
Principal transactions revenue	2,358	2,151	5,242	4,882
Corporate/Other
Principal transactions revenue
Principal transactions revenue	$ (350)	$ 340	$ (95)	$ 548