BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment reporting information
Revenues, net of interest expense	$ 18,173	$ 17,760	$ 54,194	$ 52,863
Provision (benefits) for income taxes	1,866	1,733	5,524	4,935
Income (loss) from continuing operations	4,137	3,887	12,138	11,442
Identifiable assets	1,889,133		1,889,133		$ 1,792,077
Provisions for credit losses and for benefits and claims	1,999	1,736	5,378	5,190
Operating Segments | Citicorp | North America
Segment reporting information
Revenues, net of interest expense	8,900	8,400	25,800	24,200
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenues, net of interest expense	2,700	2,500	8,300	7,300
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenues, net of interest expense	2,400	2,200	7,000	6,700
Operating Segments | Citicorp | Asia
Segment reporting information
Revenues, net of interest expense	3,700	3,500	10,800	10,400
Operating Segments | Global Consumer Banking
Segment reporting information
Revenues, net of interest expense	8,433	8,164	24,285	23,552
Provision (benefits) for income taxes	636	677	1,867	1,978
Income (loss) from continuing operations	1,174	1,250	3,306	3,729
Identifiable assets	419,000		419,000		412,000
Provisions for credit losses and for benefits and claims	2,200	1,800	5,800	4,700
Operating Segments | Institutional Clients Group
Segment reporting information
Revenues, net of interest expense	9,231	8,459	27,570	25,043
Provision (benefits) for income taxes	1,394	1,202	4,096	3,195
Income (loss) from continuing operations	3,062	2,660	8,853	7,144
Identifiable assets	1,370,000		1,370,000		1,277,000
Provisions for credit losses and for benefits and claims	(164)	(90)	(282)	382
Operating Segments | Corporate/Other
Segment reporting information
Revenues, net of interest expense	509	1,137	2,339	4,268
Provision (benefits) for income taxes	(164)	(146)	(439)	(238)
Income (loss) from continuing operations	(99)	(23)	(21)	569
Identifiable assets	100,000		100,000		$ 103,000
Provisions for credit losses and for benefits and claims	$ (50)	$ 18	$ (130)	$ 90