FAIR VALUE MEASUREMENT - Market Valuation Adjustments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Credit and funding valuation adjustments contra-liability (contra-asset)
Counterparty CVA	$ (561)	$ (580)
Asset FVA	(539)	(562)
Citigroup (own credit) CVA	346	381
Liability FVA	209	255
Total CVA and FVA—derivative instruments	(545)	(506)
Credit, Funding and Debt Valuation Adjustments Gain (Loss) [Abstract]
Counterparty CVA	(63)	(31)	$ (227)
Asset FVA	68	64	(102)
Own credit CVA	(56)	(212)	157
Liability FVA	(46)	(23)	155
Total CVA and FVA—derivative instruments	(97)	(202)	(17)
DVA related to own FVO liabilities	(573)	(2,078)	2,685
Total CVA, DVA and FVA	$ (670)	$ (2,280)	$ 2,668