BUSINESS SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues, net of interest expense	$ 19,327	$ 20,731
Provision (benefits) for income taxes	2,332	580
Income (loss) from continuing operations	7,977	2,548
Identifiable assets	2,314,266		$ 2,260,090
Operating Segments | Citicorp | North America
Segment Reporting Information [Line Items]
Revenues, net of interest expense	9,300	10,200
Operating Segments | Citicorp | EMEA
Segment Reporting Information [Line Items]
Revenues, net of interest expense	3,700	3,500
Operating Segments | Citicorp | Latin America
Segment Reporting Information [Line Items]
Revenues, net of interest expense	2,100	2,600
Operating Segments | Citicorp | Asia
Segment Reporting Information [Line Items]
Revenues, net of interest expense	4,100	4,400
Operating Segments | Global Consumer Banking
Segment Reporting Information [Line Items]
Revenues, net of interest expense	7,037	8,174
Provision (benefits) for income taxes	658	(266)
Income (loss) from continuing operations	2,174	(741)
Identifiable assets	439,000		434,000
Provisions for credit losses and for benefits and claims	(200)	4,800
Operating Segments | Institutional Clients Group
Segment Reporting Information [Line Items]
Revenues, net of interest expense	12,220	12,484
Provision (benefits) for income taxes	1,736	1,044
Income (loss) from continuing operations	5,972	3,626
Identifiable assets	1,776,000		1,730,000
Provisions for credit losses and for benefits and claims	(1,800)	2,000
Corporate/Other
Segment Reporting Information [Line Items]
Revenues, net of interest expense	70	73
Provision (benefits) for income taxes	(62)	(198)
Income (loss) from continuing operations	(169)	(337)
Identifiable assets	99,000		$ 96,000
Provisions for credit losses and for benefits and claims	$ (100)	$ 200