FAIR VALUE MEASUREMENT - Market Valuation Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Credit and funding valuation adjustments contra-liability (contra-asset)
Counterparty CVA	$ (1,020)		$ (1,020)		$ (705)
Asset FVA	(718)		(718)		(433)
Citigroup (own credit) CVA	775		775		379
Liability FVA	257		257		110
Total CVA and FVA—derivative instruments	(706)		(706)		$ (649)
Credit, Funding and Debt Valuation Adjustments Gain (Loss) [Abstract]
Counterparty CVA	(10)	$ 25	(211)	$ 68
Asset FVA	(96)	(23)	(247)	71
Own credit CVA	29	34	327	(44)
Liability FVA	58	(63)	148	(52)
Total CVA and FVA—derivative instruments	(19)	(27)	17	43
DVA related to own FVO liabilities	1,159	(107)	4,800	(256)
Total CVA, DVA and FVA	$ 1,140	$ (134)	$ 4,817	$ (213)