PRINCIPAL TRANSACTIONS (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Principal transactions revenue
Principal transactions revenue	[1]	$ 2,173	$ 1,843	$ 4,144	$ 4,731
Interest rate contracts
Principal transactions revenue
Principal transactions revenue		1,393	939	2,590	2,329
Foreign exchange contracts
Principal transactions revenue
Principal transactions revenue		718	625	804	1,173
Equity contracts
Principal transactions revenue
Principal transactions revenue		(185)	(92)	(71)	46
Commodity and other contracts
Principal transactions revenue
Principal transactions revenue		117	98	434	322
Credit products and derivatives
Principal transactions revenue
Principal transactions revenue		130	273	387	861
Operating Segments | Citicorp
Principal transactions revenue
Principal transactions revenue		2,136	1,747	4,086	4,543
Operating Segments | Institutional Clients Group
Principal transactions revenue
Principal transactions revenue		1,797	1,577	3,996	4,181
Operating Segments | Global Consumer Banking
Principal transactions revenue
Principal transactions revenue		157	170	330	342
Operating Segments | Corporate/Other
Principal transactions revenue
Principal transactions revenue		182	0	(240)	20
Operating Segments | Citi Holdings
Principal transactions revenue
Principal transactions revenue		$ 37	$ 96	$ 58	$ 188

[1] Certain prior-period revenue and expense lines and totals were reclassified to conform to the current period’s presentation. See Note 3 to the Consolidated Financial Statements.