BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment reporting information
Revenues, net of interest expense	$ 18,872	$ 18,366
Provision (benefits) for income taxes	1,441	1,863
Income (loss) from continuing operations	4,649	4,118
Identifiable assets	1,922,104		$ 1,842,465
Provisions for credit losses and for benefits and claims	1,857	1,662
Corporate/Other
Segment reporting information
Revenues, net of interest expense	591	1,201
Provision (benefits) for income taxes	(69)	(94)
Income (loss) from continuing operations	(74)	109
Identifiable assets	92,000		78,000
Provisions for credit losses and for benefits and claims	(7)	52
Operating Segments | Citicorp | North America
Segment reporting information
Revenues, net of interest expense	8,400	8,500
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenues, net of interest expense	3,200	2,900
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenues, net of interest expense	2,600	2,300
Operating Segments | Citicorp | Asia
Segment reporting information
Revenues, net of interest expense	4,100	3,500
Operating Segments | Global Consumer Banking
Segment reporting information
Revenues, net of interest expense	8,433	7,846
Provision (benefits) for income taxes	453	582
Income (loss) from continuing operations	1,394	998
Identifiable assets	423,000		428,000
Provisions for credit losses and for benefits and claims	1,900	1,800
Operating Segments | Institutional Clients Group
Segment reporting information
Revenues, net of interest expense	9,848	9,319
Provision (benefits) for income taxes	1,057	1,375
Income (loss) from continuing operations	3,329	3,011
Identifiable assets	1,407,000		$ 1,336,000
Provisions for credit losses and for benefits and claims	$ (41)	$ (205)