REGULATORY CAPITAL (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
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.	$ 5,500	$ 16,300
Citibank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 Capital	153,483	147,109
Tier 1 Capital	155,613	149,238
Quarterly Adjusted Average Total Assets	1,726,312	1,666,609
Total Leverage Exposure	$ 2,195,386	$ 2,166,334
CET1 Capital ratio	13.83%	13.92%
CET1 Capital ratio, well capitalized minimum	6.50%
Tier 1 Capital ratio, well capitalized minimum	0.080
Tier 1 Capital ratio	0.1403	0.1412
Total Capital ratio, well capitalized minimum	0.100
Total Capital ratio	0.1493	0.1520
Tier 1 Leverage ratio	0.0901	0.0895
Tier 1 Leverage ratio, well capitalized minimum	0.050
Supplementary leverage ratio	0.0709	0.0689
Supplementary leverage ratio, well capitalized minimum	6.00%
Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 Capital	$ 155,363	$ 153,595
Tier 1 Capital	174,527	172,504
Quarterly Adjusted Average Total Assets	2,433,364	2,394,272
Total Leverage Exposure	$ 2,985,418	$ 2,964,954
CET1 Capital ratio	13.63%	13.37%
Tier 1 Capital ratio, well capitalized minimum	0.060
Tier 1 Capital ratio	0.1531	0.1502
Total Capital ratio, well capitalized minimum	0.100
Total Capital ratio	0.1542	0.1513
Tier 1 Leverage ratio	0.0717	0.0720
Supplementary leverage ratio	0.0585	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)	$ 173,060	$ 168,571
Total Risk-Weighted Assets	998,817	983,960
Standardized Approach | Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	205,827	201,768
Total Risk-Weighted Assets	1,139,988	1,148,608
Advanced Approach | Citibank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	165,581	160,706
Total Risk-Weighted Assets	1,109,387	1,057,194
Advanced Approach | Citigroup Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital (Tier 1 Capital and Tier 2 Capital)	197,371	191,919
Total Risk-Weighted Assets	$ 1,280,190	$ 1,268,723