SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Variable Interest Entity
Total involvement with SPE assets	$ 475,664	$ 511,990
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	66,188	62,201
Significant unconsolidated VIE assets	409,476	449,789
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	58,909	50,861
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,691	4,170
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	16,883	15,322
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	136	61
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	79,619	70,414
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	6,000	69,000
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	282	498
Venture capital funds
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	8,500	33,600
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	31,852	32,021
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	31,852	32,021
Significant unconsolidated VIE assets	0	0
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	0	0
Mortgage-backed securities - U.S. agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	123,787	117,358
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	123,787	117,358
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,332	2,052
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	136	48
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,468	2,100
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	64,963	67,704
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	64,963	67,704
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,751	3,294
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	129	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	3,880	3,294
Citi-administered asset-backed commercial paper conduits
Variable Interest Entity
Total involvement with SPE assets	21,097	19,621
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	21,097	19,621
Significant unconsolidated VIE assets	0	0
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	0	0
Collateralized loan obligations (CLOs)
Variable Interest Entity
Total involvement with SPE assets	5,562	7,600
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	5,562	7,600
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,344	2,601
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,344	2,601
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	204,680	242,348
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	12,197	9,672
Significant unconsolidated VIE assets	192,483	232,676
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	48,187	40,121
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	902	1,022
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	13,655	10,726
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	62,744	51,869
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	1,493	2,155
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	883	672
Significant unconsolidated VIE assets	610	1,483
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	12	2
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	417	1,108
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	429	1,110
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	21,317	22,167
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	3	3
Significant unconsolidated VIE assets	21,314	22,164
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,243	2,731
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	2,779	3,143
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,587	3,420
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	7,609	9,294
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	368	482
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	86	121
Significant unconsolidated VIE assets	282	361
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	37	58
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	13
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	37	71
Investment funds
Variable Interest Entity
Total involvement with SPE assets	545	534
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	70	91
Significant unconsolidated VIE assets	475	443
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3	2
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	10	5
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	95	68
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	108	75
Other
Variable Interest Entity
Total involvement with SPE assets	0	0
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	0	0
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	$ 0	$ 0