BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment reporting information
Revenue	$ 18,469	$ 18,155	$ 37,341	$ 36,521
Provision (benefits) for income taxes	1,444	1,795	2,885	3,658
Income (loss) from continuing operations	4,501	3,883	9,150	8,001
Identifiable assets	1,912,334		1,912,334		$ 1,842,465
Provisions for credit losses and for benefits and claims	1,812	1,717	3,669	3,379
Corporate/Other
Segment reporting information
Revenue	528	661	1,119	1,862
Provision (benefits) for income taxes	62	(178)	(7)	(272)
Income (loss) from continuing operations	(15)	(25)	(89)	84
Identifiable assets	93,000		93,000		78,000
Provisions for credit losses and for benefits and claims	(118)	(132)	(125)	(80)
Operating Segments | Citicorp | North America
Segment reporting information
Revenue	8,600	8,600	16,900	17,200
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenue	3,000	2,900	6,200	5,700
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenue	2,500	2,400	5,100	4,700
Operating Segments | Citicorp | Asia
Segment reporting information
Revenue	3,800	3,600	8,000	7,100
Operating Segments | Global Consumer Banking
Segment reporting information
Revenue	8,250	8,073	16,683	15,919
Provision (benefits) for income taxes	411	646	864	1,228
Income (loss) from continuing operations	1,279	1,128	2,673	2,126
Identifiable assets	422,000		422,000		428,000
Provisions for credit losses and for benefits and claims	1,900	1,800	3,800	3,600
Operating Segments | Institutional Clients Group
Segment reporting information
Revenue	9,691	9,421	19,539	18,740
Provision (benefits) for income taxes	971	1,327	2,028	2,702
Income (loss) from continuing operations	3,237	2,780	6,566	5,791
Identifiable assets	1,397,000		1,397,000		$ 1,336,000
Provisions for credit losses and for benefits and claims	$ 25	$ 87	$ (16)	$ (118)