SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Assets and Liabilities of VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Cash and due from banks	$ 22,782	$ 27,342	$ 30,577
Trading account assets	442,747	411,756
Investments	476,657	519,085
Loans, net of unearned income	694,488	689,362
Allowance for credit losses on loans (ACLL)	(18,574)	(18,145)	(16,974)	$ (16,455)
Total loans, net	675,914	671,217
Other assets	102,206	95,963
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	60,039	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	48,505	37,457
Long-term debt	287,300	286,619
Other liabilities	68,114	75,835
Total liabilities	2,143,579	2,205,583
Consumer
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	393,102	389,197
Allowance for credit losses on loans (ACLL)	(16,018)	(15,431)	(14,119)	(14,040)
Corporate
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	301,386	300,165
Allowance for credit losses on loans (ACLL)	(2,556)	(2,714)	$ (2,855)	$ (2,415)
Variable Interest Entity, Primary Beneficiary
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Cash and due from banks	65	44
Trading account assets	6,971	11,350
Investments	739	767
Loans, net of unearned income	54,450	56,348
Allowance for credit losses on loans (ACLL)	(2,376)	(2,481)
Total loans, net	52,074	53,867
Other assets	190	160
Liabilities of consolidated VIEs for which creditors or beneficial interest holders do not have recourse to the general credit of Citigroup
Short-term borrowings	13,628	9,692
Long-term debt	5,271	8,443
Other liabilities	920	927
Total liabilities	19,819	19,062
Variable Interest Entity, Primary Beneficiary | Consumer
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	32,958	35,141
Variable Interest Entity, Primary Beneficiary | Corporate
Assets of consolidated VIEs to be used to settle obligations of consolidated VIEs
Loans, net of unearned income	$ 21,492	$ 21,207