INVESTMENTS - Recognition and Measurement of Impairment Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
AFS debt securities
OTTI on Investments disclosures
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	$ 188	$ 360	$ 181

The aggregate amount (i) of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis and OTTI losses recognized during the period on investments accounted for under the cost method of accounting.; and (ii) of an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting.

No definition available.

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