FAIR VALUE MEASUREMENT - Market Valuation Adjustments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Credit and funding valuation adjustments contra-liability (contra-asset)
Counterparty CVA	$ (771)		$ (816)
Asset FVA	(593)		(622)
Citigroup (own credit) CVA	564		607
Liability FVA	235		263
Total CVA and FVA—derivative instruments	(565)		$ (568)
Credit, Funding and Debt Valuation Adjustments Gain (Loss) [Abstract]
Counterparty CVA	(34)	$ (107)
Asset FVA	(6)	(105)
Own credit CVA	(35)	116
Liability FVA	(28)	22
Total CVA and FVA—derivative instruments	(103)	(74)
DVA related to own FVO liabilities	(433)	1,050
Total CVA, DVA and FVA	$ (536)	$ 976