INVESTMENTS - Recognition and Measurement of Impairment (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Impairment losses recognized in earnings for debt securities that the Company intends to sell, would more-likely-than-not be required to sell or will be subject to an issuer call deemed probable of exercise	$ 13	$ 43	$ 36	$ 137

For investments that the entity does intend to sell or will more-likely-than-not be required to sell before recovery, the amount by which the fair value of an investment is less than the amortized cost basis or carrying amount at the balance sheet date and the decline in fair value is deemed to be other than temporary, the amount recognized in earnings for securities.

No definition available.

Name:	c_OtherThanTemporaryImpairmentLossesInvestmentsWithIntentToSell
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration