FAIR VALUE MEASUREMENT - Market Valuation Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Credit and funding valuation adjustments contra-liability (contra-asset)
Counterparty CVA	$ (849)		$ (849)		$ (705)
Asset FVA	(625)		(625)		(433)
Citigroup (own credit) CVA	746		746		379
Liability FVA	199		199		110
Total CVA and FVA—derivative instruments	(529)		(529)		$ (649)
Credit, Funding and Debt Valuation Adjustments Gain (Loss) [Abstract]
Counterparty CVA	(94)	$ 34	(201)	$ 43
Asset FVA	(46)	25	(151)	94
Own credit CVA	182	(41)	298	(78)
Liability FVA	68	(13)	90	11
Total CVA and FVA—derivative instruments	110	5	36	70
DVA related to own FVO liabilities	2,592	(110)	3,642	(148)
Total CVA, DVA and FVA	$ 2,702	$ (105)	$ 3,678	$ (78)