SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Variable Interest Entity
Total involvement with SPE assets	$ 528,659	$ 475,664
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	60,039	66,188
Significant unconsolidated VIE assets	468,620	409,476
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	64,618	58,909
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,483	3,691
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	16,351	16,883
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	172	136
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	84,624	79,619
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	45,500	6,000
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	824	282
Venture capital funds
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	8,100	8,500
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	29,746	31,852
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	29,746	31,852
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	120,568	123,787
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	120,568	123,787
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,387	2,332
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	123	136
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,510	2,468
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	62,378	64,963
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	62,378	64,963
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,479	3,751
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	566	129
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	4,045	3,880
Citi-administered asset-backed commercial paper conduits
Variable Interest Entity
Total involvement with SPE assets	21,306	21,097
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	21,306	21,097
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	3,920	5,562
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	0	0
Significant unconsolidated VIE assets	3,920	5,562
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,019	2,344
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	2,019	2,344
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	268,498	204,680
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	7,947	12,197
Significant unconsolidated VIE assets	260,551	192,483
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	54,349	48,187
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	735	902
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	13,185	13,655
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	68,269	62,744
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	935	1,493
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	935	883
Significant unconsolidated VIE assets	0	610
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	0	12
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	417
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	429
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	20,280	21,317
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	3	3
Significant unconsolidated VIE assets	20,277	21,314
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,360	2,243
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	2,730	2,779
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,502	2,587
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	7,592	7,609
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	387	368
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	81	86
Significant unconsolidated VIE assets	306	282
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	20	37
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	49	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	69	37
Investment funds
Variable Interest Entity
Total involvement with SPE assets	641	545
Total assets of consolidated VIEs to be used to settle obligations of consolidated VIEs	21	70
Significant unconsolidated VIE assets	620	475
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	4	3
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	18	10
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	98	95
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	$ 120	$ 108