SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Assets and Liabilities of VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Cash and due from banks	$ 27,342	$ 30,577	$ 27,515
Trading account assets	411,756	334,114
Investments	519,085	526,582
Loans, net of unearned income	689,362	657,221
Allowance for credit losses on loans (ACLL)	(18,145)	(16,974)	(16,455)	$ (24,956)
Total loans, net	671,217	640,247
Other assets	95,963	103,743
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	66,188	62,201
Liabilities of consolidated VIEs for which creditors or beneficial interest holders do not have recourse to the general credit of Citigroup
Short-term borrowings	37,457	47,096
Long-term debt	286,619	271,606
Other liabilities	75,835	87,873
Total liabilities	2,205,583	2,214,838
Consumer
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	389,197	368,067
Allowance for credit losses on loans (ACLL)	(15,431)	(14,119)	(14,040)	(20,180)
Corporate
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	300,165	289,154
Allowance for credit losses on loans (ACLL)	(2,714)	(2,855)	$ (2,415)	$ (4,776)
Variable Interest Entity, Primary Beneficiary
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Cash and due from banks	44	61
Trading account assets	11,350	9,153
Investments	767	594
Loans, net of unearned income	56,348	54,808
Allowance for credit losses on loans (ACLL)	(2,481)	(2,520)
Total loans, net	53,867	52,288
Other assets	160	105
Liabilities of consolidated VIEs for which creditors or beneficial interest holders do not have recourse to the general credit of Citigroup
Short-term borrowings	9,692	9,807
Long-term debt	8,443	10,324
Other liabilities	927	622
Total liabilities	19,062	20,753
Variable Interest Entity, Primary Beneficiary | Consumer
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	35,141	35,026
Variable Interest Entity, Primary Beneficiary | Corporate
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	$ 21,207	$ 19,782