BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment reporting information
Revenues, net of interest expense	$ 18,758	$ 18,469	$ 37,334	$ 37,341
Provision (benefits) for income taxes	1,373	1,444	2,648	2,885
Income (loss) from continuing operations	4,792	4,501	9,529	9,150
Identifiable assets	1,988,226		1,988,226		$ 1,917,383
Provisions for credit losses and for benefits and claims	2,093	1,812	4,073	3,669
Operating Segments | Citicorp | North America
Segment reporting information
Revenues, net of interest expense	8,600	8,600	17,000	16,900
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenues, net of interest expense	3,000	3,000	6,100	6,200
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenues, net of interest expense	2,600	2,500	5,200	5,100
Operating Segments | Citicorp | Asia
Segment reporting information
Revenues, net of interest expense	4,000	3,800	8,100	8,000
Operating Segments | Global Consumer Banking
Segment reporting information
Revenues, net of interest expense	8,505	8,244	16,956	16,670
Provision (benefits) for income taxes	417	411	839	865
Income (loss) from continuing operations	1,413	1,276	2,850	2,666
Identifiable assets	437,000		437,000		432,000
Provisions for credit losses and for benefits and claims	2,000	1,900	4,000	3,800
Operating Segments | Institutional Clients Group
Segment reporting information
Revenues, net of interest expense	9,721	9,697	19,415	19,552
Provision (benefits) for income taxes	919	971	1,843	2,027
Income (loss) from continuing operations	3,343	3,241	6,665	6,575
Identifiable assets	1,454,000		1,454,000		1,394,000
Provisions for credit losses and for benefits and claims	103	25	124	(16)
Corporate/Other
Segment reporting information
Revenues, net of interest expense	532	528	963	1,119
Provision (benefits) for income taxes	37	62	(34)	(7)
Income (loss) from continuing operations	36	(16)	14	(91)
Identifiable assets	97,000		97,000		$ 91,000
Provisions for credit losses and for benefits and claims	$ (22)	$ (118)	$ (47)	$ (125)