BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues, net of interest expense	$ 17,302	$ 18,574	$ 57,799	$ 55,908
Provision (benefits) for income taxes	815	1,079	1,522	3,727
Income (loss) from continuing operations	3,261	4,943	7,112	14,472
Identifiable assets	2,234,459		2,234,459		$ 1,951,158
Operating Segments | Citicorp | North America
Segment Reporting Information [Line Items]
Revenues, net of interest expense	8,400	8,400	28,300	25,300
Operating Segments | Citicorp | EMEA
Segment Reporting Information [Line Items]
Revenues, net of interest expense	3,100	3,100	9,900	9,300
Operating Segments | Citicorp | Latin America
Segment Reporting Information [Line Items]
Revenues, net of interest expense	2,200	2,600	7,000	7,700
Operating Segments | Citicorp | Asia
Segment Reporting Information [Line Items]
Revenues, net of interest expense	3,800	4,000	12,300	12,100
Operating Segments | Global Consumer Banking
Segment Reporting Information [Line Items]
Revenues, net of interest expense	7,173	8,289	22,686	24,512
Provision (benefits) for income taxes	338	468	(93)	1,227
Income (loss) from continuing operations	1,058	1,503	(95)	4,124
Identifiable assets	435,000		435,000		407,000
Provisions for credit losses and for benefits and claims	1,600	2,000	10,300	5,900
Operating Segments | Institutional Clients Group
Segment Reporting Information [Line Items]
Revenues, net of interest expense	10,353	9,851	34,974	29,924
Provision (benefits) for income taxes	818	858	2,332	2,763
Income (loss) from continuing operations	2,919	3,229	8,425	10,066
Identifiable assets	1,703,000		1,703,000		1,447,000
Provisions for credit losses and for benefits and claims	800	200	6,700	300
Corporate/Other
Segment Reporting Information [Line Items]
Revenues, net of interest expense	(224)	434	139	1,472
Provision (benefits) for income taxes	(341)	(247)	(717)	(263)
Income (loss) from continuing operations	(716)	211	(1,218)	282
Identifiable assets	96,000		96,000		$ 97,000
Provisions for credit losses and for benefits and claims	$ (100)	$ (0)	$ 220	$ (62)