SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Variable Interest Entity
Total involvement with SPE assets	$ 635,338	$ 528,659
Consolidated VIE/SPE assets	2,642,475	2,352,945
Significant unconsolidated VIE assets	577,622	468,620
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	70,083	64,618
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,502	3,483
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	19,640	16,351
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	180	172
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	93,405	84,624
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	125,100	45,500
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	1,191	824
Private equity
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	9,100	8,100
Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	57,716	60,039
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	27,489	29,746
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
Credit card securitizations | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	27,489	29,746
Mortgage securitizations - U.S. agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	123,762	120,568
Significant unconsolidated VIE assets	123,762	120,568
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,391	2,387
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	115	123
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	3,506	2,510
Mortgage securitizations - U.S. agency-sponsored | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	0	0
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	66,430	62,378
Significant unconsolidated VIE assets	66,430	62,378
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	4,204	3,479
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	234	566
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	4,438	4,045
Mortgage securitizations - Non-agency-sponsored | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	0	0
Citi-administered asset-backed commercial paper conduits
Variable Interest Entity
Total involvement with SPE assets	19,037	21,306
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
Citi-administered asset-backed commercial paper conduits | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	19,037	21,306
Collateralized loan obligations (CLOs)
Variable Interest Entity
Total involvement with SPE assets	731	3,920
Significant unconsolidated VIE assets	731	3,920
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	227	2,019
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	227	2,019
Collateralized loan obligations (CLOs) | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	0	0
Asset-backed securities
Variable Interest Entity
Total involvement with SPE assets	369,331	268,498
Significant unconsolidated VIE assets	361,033	260,551
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	59,862	54,349
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	638	735
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	15,940	13,185
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	76,440	68,269
Asset-backed securities | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	8,298	7,947
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	2,802	935
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
Municipal securities tender option bond trusts (TOBs) | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	2,802	935
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	21,725	20,280
Significant unconsolidated VIE assets	21,725	20,277
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,392	2,360
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	2,817	2,730
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,374	2,502
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	8,583	7,592
Municipal investments | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	0	3
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	196	387
Significant unconsolidated VIE assets	112	306
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3	20
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	52	49
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	55	69
Client intermediation | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	84	81
Investment funds
Variable Interest Entity
Total involvement with SPE assets	3,835	641
Significant unconsolidated VIE assets	3,829	620
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	4	4
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	47	18
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	92	98
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	13	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	156	120
Investment funds | Consolidated VIEs
Variable Interest Entity
Consolidated VIE/SPE assets	$ 6	$ 21