DEBT - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument
Weighted average interest rate	4.17%
Long-term debt	$ 286,619	$ 271,606
Weighted average interest rate after effect of derivative contract	4.22%
Senior debt
Debt Instrument
Long-term debt	$ 259,889	247,242
Subordinated debt
Debt Instrument
Long-term debt	25,116	22,758
Trust preferred securities
Debt Instrument
Long-term debt	1,614	1,606
Citigroup Inc.
Debt Instrument
Long-term debt	$ 162,309	166,257
Citigroup Inc. | Senior debt
Debt Instrument
Weighted average interest rate	3.53%
Long-term debt	$ 135,579	141,893
Citigroup Inc. | Subordinated debt
Debt Instrument
Weighted average interest rate	5.02%
Long-term debt	$ 25,116	22,758
Citigroup Inc. | Trust preferred securities
Debt Instrument
Weighted average interest rate	11.66%
Long-term debt	$ 1,614	1,606
Bank
Debt Instrument
Long-term debt	$ 31,673
Bank | Senior debt
Debt Instrument
Weighted average interest rate	5.37%
Long-term debt	$ 31,673	21,113
Collateralized long-term advances from Federal Home Loan Bank	11,500	7,300
Broker-dealer
Debt Instrument
Long-term debt	$ 92,637
Broker-dealer | Senior debt
Debt Instrument
Weighted average interest rate	5.34%
Long-term debt	$ 92,637	$ 84,236