BUSINESS SEGMENTS (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($) country	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) country	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment reporting information
Revenues, net of interest expense	$ 16,499	$ 17,302	$ 19,766	$ 20,731	$ 18,378	$ 18,574	$ 18,758	$ 18,576	$ 74,298	$ 74,286	$ 72,854
Provision (benefits) for income taxes	1,116	777	52	580	703	1,079	1,373	1,275	2,525	4,430	5,357
Income (loss) from continuing operations	4,325	$ 3,177	$ 1,057	$ 2,548	4,999	$ 4,943	$ 4,792	$ 4,737	11,107	19,471	18,088
Identifiable assets	2,260,090				1,951,158				2,260,090	1,951,158
Operating Segments | Citicorp | North America
Segment reporting information
Revenues, net of interest expense									36,300	33,900	33,400
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenues, net of interest expense									12,800	12,000	11,800
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenues, net of interest expense									9,200	10,400	10,300
Operating Segments | Citicorp | Asia
Segment reporting information
Revenues, net of interest expense									15,900	16,000	15,300
Operating Segments | Global Consumer Banking
Segment reporting information
Revenues, net of interest expense									29,991	32,971	32,339
Provision (benefits) for income taxes									212	1,746	1,689
Income (loss) from continuing operations									874	5,702	5,309
Identifiable assets	$ 434,000				407,000				434,000	407,000
Provision for credit losses									$ 11,700	7,900	7,600
Operating Segments | Institutional Clients Group
Segment reporting information
Number of countries where the entity provides a broad range of banking and financial products and services (over) | country	96								96
Revenues, net of interest expense									$ 44,253	39,301	38,325
Provision (benefits) for income taxes									3,373	3,570	3,756
Income (loss) from continuing operations									11,798	12,944	12,574
Identifiable assets	$ 1,730,000				1,447,000				1,730,000	1,447,000
Provision for credit losses									5,600	600	200
Corporate/Other
Segment reporting information
Revenues, net of interest expense									54	2,014	2,190
Provision (benefits) for income taxes									(1,060)	(886)	(88)
Income (loss) from continuing operations									(1,565)	825	205
Identifiable assets	$ 96,000				$ 97,000				96,000	97,000
Provision for credit losses									$ 200	$ (100)	$ (200)