SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Assets and Liabilities of VIEs (Details) - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Cash and due from banks	$ 26,917		$ 27,342	$ 25,763
Trading account assets	446,339		411,756
Investments	508,276		519,085
Loans, net of unearned income	687,722		689,362
Allowance for credit losses on loans (ACLL)	(18,216)	$ (18,296)	(18,145)	(17,496)	$ (17,169)	$ (16,974)
Total loans, net	669,506		671,217
Other assets, at fair value	99,569		95,963
Total assets	2,405,686		2,411,834
Liabilities of consolidated VIEs for which creditors or beneficial interest holders do not have recourse to the general credit of Citigroup
Short-term borrowings	38,694		37,457
Long-term debt	280,321		286,619
Other liabilities	69,304		75,835
Total liabilities	2,196,542		2,205,583
Consumer loans
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	386,117		389,197
Allowance for credit losses on loans (ACLL)	(15,732)	(15,524)	(15,431)	(14,866)	(14,389)	(14,119)
Corporate loans
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	301,605		300,165
Allowance for credit losses on loans (ACLL)	(2,484)	$ (2,772)	(2,714)	$ (2,630)	$ (2,780)	$ (2,855)
Consolidated VIEs
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Cash and due from banks	71		44
Trading account assets	7,920		11,350
Investments	923		767
Loans, net of unearned income	53,169		56,348
Allowance for credit losses on loans (ACLL)	(2,558)		(2,481)
Total loans, net	50,611		53,867
Other assets, at fair value	157		160
Total assets	59,682		66,188
Liabilities of consolidated VIEs for which creditors or beneficial interest holders do not have recourse to the general credit of Citigroup
Short-term borrowings	9,754		9,692
Long-term debt	6,085		8,443
Other liabilities	1,438		927
Total liabilities	17,277		19,062
Consolidated VIEs | Consumer loans
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	32,956		35,141
Consolidated VIEs | Corporate loans
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	$ 20,213		$ 21,207