FAIR VALUE MEASUREMENT - Market Valuation Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Credit and funding valuation adjustments contra-liability (contra-asset)
Counterparty CVA	$ (651)		$ (651)		$ (816)
Asset FVA	(502)		(502)		(622)
Citigroup (own credit) CVA	456		456		607
Liability FVA	219		219		263
Total CVA and FVA—derivative instruments	(478)		(478)		$ (568)
Credit, Funding and Debt Valuation Adjustments Gain (Loss) [Abstract]
Counterparty CVA	4	$ (94)	(30)	$ (201)
Asset FVA	100	(46)	94	(151)
Own credit CVA	(114)	182	(149)	298
Liability FVA	(17)	68	(44)	90
Total CVA and FVA—derivative instruments	(27)	110	(129)	36
DVA related to own FVO liabilities	(837)	2,592	(1,270)	3,642
Total CVA, DVA and FVA	$ (864)	$ 2,702	$ (1,399)	$ 3,678