BUSINESS SEGMENTS (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting [Abstract]
Number of business segments | segment			2
Segment Reporting Information [Line Items]
Revenues, net of interest expense	$ 17,474	$ 19,766	$ 36,801	$ 40,497
Provision (benefits) for income taxes	1,155	52	3,487	632
Income (loss) from continuing operations	6,193	1,057	14,170	3,605
Identifiable assets	2,327,868		2,327,868		$ 2,260,090
Operating Segments | Citicorp | North America
Segment Reporting Information [Line Items]
Revenues, net of interest expense	7,900	9,700	17,200	19,900
Operating Segments | Citicorp | EMEA
Segment Reporting Information [Line Items]
Revenues, net of interest expense	3,300	3,400	7,000	6,900
Operating Segments | Citicorp | Latin America
Segment Reporting Information [Line Items]
Revenues, net of interest expense	2,200	2,300	4,400	4,900
Operating Segments | Citicorp | Asia
Segment Reporting Information [Line Items]
Revenues, net of interest expense	3,800	4,100	7,900	8,500
Operating Segments | Global Consumer Banking
Segment Reporting Information [Line Items]
Revenues, net of interest expense	6,820	7,339	13,857	15,513
Provision (benefits) for income taxes	573	(257)	1,230	(538)
Income (loss) from continuing operations	1,832	(705)	4,003	(1,489)
Identifiable assets	432,000		432,000		434,000
Provisions for credit losses and for benefits and claims	(100)	4,200	(300)	8,900
Operating Segments | Institutional Clients Group
Segment Reporting Information [Line Items]
Revenues, net of interest expense	10,387	12,137	22,607	24,621
Provision (benefits) for income taxes	1,104	455	2,830	1,484
Income (loss) from continuing operations	3,829	1,822	9,767	5,396
Identifiable assets	1,795,000		1,795,000		1,730,000
Provisions for credit losses and for benefits and claims	(800)	3,900	(2,600)	5,900
Corporate/Other
Segment Reporting Information [Line Items]
Revenues, net of interest expense	267	290	337	363
Provision (benefits) for income taxes	(522)	(146)	(573)	(314)
Income (loss) from continuing operations	532	(60)	400	(302)
Identifiable assets	101,000		101,000		$ 96,000
Provisions for credit losses and for benefits and claims	$ (100)	$ 200	$ (200)	$ 400