PRINCIPAL TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Principal transactions revenue
Principal transactions revenue	$ 2,170	$ 2,238	$ 7,754	$ 5,894
Interest rate risks
Principal transactions revenue
Principal transactions revenue	1,120	1,282	4,297	3,229
Foreign exchange risks
Principal transactions revenue
Principal transactions revenue	610	466	2,000	1,481
Equity risks
Principal transactions revenue
Principal transactions revenue	158	81	404	76
Commodity and other risks
Principal transactions revenue
Principal transactions revenue	92	171	330	436
Credit products and risks
Principal transactions revenue
Principal transactions revenue	190	238	723	672
Citicorp | Operating Segments
Principal transactions revenue
Principal transactions revenue	2,170	2,238	7,754	5,894
Global Consumer Banking | Operating Segments
Principal transactions revenue
Principal transactions revenue	149	162	440	469
Institutional Clients Group | Operating Segments
Principal transactions revenue
Principal transactions revenue	1,757	2,064	6,504	5,552
Corporate/Other | Operating Segments
Principal transactions revenue
Principal transactions revenue	$ 264	$ 12	$ 810	$ (127)