PRINCIPAL TRANSACTIONS (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Principal transactions revenue
Principal transactions revenue	[1]	$ 1,327	$ 1,549	$ 5,471	$ 6,280
Interest rate contracts
Principal transactions revenue
Principal transactions revenue		907	911	3,497	3,240
Foreign exchange contracts
Principal transactions revenue
Principal transactions revenue		432	464	1,236	1,637
Equity contracts
Principal transactions revenue
Principal transactions revenue		(183)	(9)	(254)	37
Commodity and other contracts
Principal transactions revenue
Principal transactions revenue		180	164	614	486
Credit products and derivatives
Principal transactions revenue
Principal transactions revenue		(9)	19	378	880
Operating Segments | Citicorp
Principal transactions revenue
Principal transactions revenue		1,344	1,372	5,430	5,915
Operating Segments | Institutional Clients Group
Principal transactions revenue
Principal transactions revenue		1,209	1,396	5,205	5,577
Operating Segments | Global Consumer Banking
Principal transactions revenue
Principal transactions revenue		161	199	491	541
Operating Segments | Corporate/Other
Principal transactions revenue
Principal transactions revenue		(26)	(223)	(266)	(203)
Operating Segments | Citi Holdings
Principal transactions revenue
Principal transactions revenue		$ (17)	$ 177	$ 41	$ 365

[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.