REGULATORY CAPITAL - Regulatory Capital Compliance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 Capital ratio, stated minimum	4.50%
Tier 1 Capital ratio, stated minimum	0.060
Total Capital ratio, stated minimum	0.080
Tier 1 Leverage ratio, stated minimum	0.040
Supplementary leverage ratio, stated minimum	3.00%
Dividends received from Citibank N.A.	$ 16,300	$ 8,500
Citibank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 Capital	147,109	149,593
Tier 1 Capital	149,238	151,720
Quarterly Adjusted Average Total Assets	1,666,609	1,738,744
Total Leverage Exposure	$ 2,166,334	$ 2,189,541
CET1 Capital ratio	13.92%	14.90%
CET1 Capital ratio, well capitalized minimum	6.50%
Tier 1 Capital ratio, well capitalized minimum	0.080
Tier 1 Capital ratio	0.1412	0.1512
Total Capital ratio, well capitalized minimum	0.100
Total Capital ratio	0.1520	0.1645
Tier 1 Leverage ratio	0.0895	0.0873
Tier 1 Leverage ratio, well capitalized minimum	0.050
Supplementary leverage ratio	0.0689	0.0693
Supplementary leverage ratio, well capitalized minimum	6.00%
Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 Capital	$ 153,595	$ 148,930
Tier 1 Capital	172,504	169,145
Quarterly Adjusted Average Total Assets	2,394,272	2,395,863
Total Leverage Exposure	$ 2,964,954	$ 2,906,773
CET1 Capital ratio	13.37%	13.03%
Tier 1 Capital ratio, well capitalized minimum	0.060
Tier 1 Capital ratio	0.1502	0.1480
Total Capital ratio, well capitalized minimum	0.100
Total Capital ratio	0.1513	0.1546
Tier 1 Leverage ratio	0.0720	0.0706
Supplementary leverage ratio	0.0582	0.0582
Standardized Approach | Citibank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	$ 168,571	$ 172,647
Total Risk-Weighted Assets	983,960	982,914
Standardized Approach | Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	201,768	197,543
Total Risk-Weighted Assets	1,148,608	1,142,985
Advanced Approach | Citibank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	160,706	165,131
Total Risk-Weighted Assets	1,057,194	1,003,747
Advanced Approach | Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	191,919	188,839
Total Risk-Weighted Assets	$ 1,268,723	$ 1,221,538