BUSINESS SEGMENTS (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) country	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) country		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)
Segment reporting information
Revenues, net of interest expense	$ 17,124	$ 18,389	$ 18,469	$ 18,872	$ 17,504	$ 18,419	$ 18,155	$ 18,366	$ 72,854	[1]	$ 72,444	[1]	$ 70,797	[1]
Provision (benefits) for income taxes	1,001	1,471	1,444	1,441	23,864	1,866	1,795	1,863	5,357		29,388		6,444
Income (loss) from continuing operations	4,305	4,633	4,501	4,649	(18,765)	4,137	3,883	4,118	18,088		(6,627)		15,033
Identifiable assets	1,917,383				1,842,465				1,917,383		1,842,465
Provisions for credit losses and for benefits and claims	1,925	$ 1,974	$ 1,812	$ 1,857	2,073	$ 1,999	$ 1,717	$ 1,662	7,568		7,451		6,982
Operating Segments | Citicorp | North America
Segment reporting information
Revenues, net of interest expense									33,400		34,200		32,600
Operating Segments | Citicorp | EMEA
Segment reporting information
Revenues, net of interest expense									11,800		10,900		10,000
Operating Segments | Citicorp | Latin America
Segment reporting information
Revenues, net of interest expense									10,300		9,600		9,100
Operating Segments | Citicorp | Asia
Segment reporting information
Revenues, net of interest expense									15,300		14,600		13,900
Operating Segments | Global Consumer Banking
Segment reporting information
Revenues, net of interest expense									33,777		32,838		31,624
Provision (benefits) for income taxes									1,839		3,316		2,639
Income (loss) from continuing operations									5,762		3,878		4,931
Identifiable assets	$ 432,000				428,000				432,000		428,000
Provisions for credit losses and for benefits and claims									$ 7,600		7,600		6,400
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	98								98
Revenues, net of interest expense									$ 36,994		36,474		33,940
Provision (benefits) for income taxes									3,631		7,008		4,260
Income (loss) from continuing operations									12,200		9,066		9,525
Identifiable assets	$ 1,394,000				1,336,000				1,394,000		1,336,000
Provisions for credit losses and for benefits and claims									184		(15)		486
Operating Segments | Corporate/Other
Segment reporting information
Revenues, net of interest expense									2,083		3,132		5,233
Provision (benefits) for income taxes									(113)		19,064		(455)
Income (loss) from continuing operations									126		(19,571)		577
Identifiable assets	$ 91,000				$ 78,000				91,000		78,000
Provisions for credit losses and for benefits and claims									$ 202		$ (175)		$ 69

[1] Certain prior-period revenue and expense lines and totals were reclassified to conform to the current period’s presentation. See Notes 1 and 3 to the Consolidated Financial Statements.