FAIR VALUE MEASUREMENT - Market Valuation Adjustments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Credit and funding valuation adjustments contra-liability (contra-asset)
Counterparty CVA	$ (580)	$ (816)
Asset FVA	(562)	(622)
Citigroup (own credit) CVA	381	607
Liability FVA	255	263
Total CVA and FVA—derivative instruments	(506)	(568)
Credit, Funding and Debt Valuation Adjustments Gain (Loss) [Abstract]
Counterparty CVA	(31)	(227)	$ 79
Asset FVA	64	(102)	96
Own credit CVA	(212)	157	(33)
Liability FVA	(23)	155	(22)
Total CVA and FVA—derivative instruments	(202)	(17)	120
DVA related to own FVO liabilities	(2,078)	2,685	296
Total CVA, DVA and FVA	$ (2,280)	$ 2,668	$ 416