BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment reporting information
Revenues, net of interest expense	$ 18,576	$ 18,872
Provision (benefits) for income taxes	1,275	1,441
Income (loss) from continuing operations	4,737	4,649
Identifiable assets	1,958,413		$ 1,917,383
Provisions for credit losses and for benefits and claims	1,980	1,857
Operating Segments | Citicorp | North America
Segment reporting information
Revenues, net of interest expense	8,300	8,200
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenues, net of interest expense	3,200	3,200
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenues, net of interest expense	2,500	2,600
Operating Segments | Citicorp | Asia
Segment reporting information
Revenues, net of interest expense	4,100	4,100
Operating Segments | Global Consumer Banking
Segment reporting information
Revenues, net of interest expense	8,451	8,426
Provision (benefits) for income taxes	422	454
Income (loss) from continuing operations	1,437	1,390
Identifiable assets	426,000		432,000
Provisions for credit losses and for benefits and claims	2,000	1,900
Operating Segments | Institutional Clients Group
Segment reporting information
Revenues, net of interest expense	9,694	9,855
Provision (benefits) for income taxes	924	1,056
Income (loss) from continuing operations	3,322	3,334
Identifiable assets	1,425,000		1,394,000
Provisions for credit losses and for benefits and claims	21	(41)
Corporate/Other
Segment reporting information
Revenues, net of interest expense	431	591
Provision (benefits) for income taxes	(71)	(69)
Income (loss) from continuing operations	(22)	(75)
Identifiable assets	107,000		$ 91,000
Provisions for credit losses and for benefits and claims	$ (25)	$ (7)