SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Variable Interest Entity
Total involvement with SPE assets	$ 511,990	$ 500,212
Consolidated VIE / SPE assets	62,201	58,637
Significant unconsolidated VIE assets	449,789	441,575
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	50,861	41,528
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	4,170	4,756
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	15,322	17,266
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	61	268
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	70,414	63,818
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	69,000	100,000
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	498	497
Venture capital funds
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	33,600	55,600
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	32,021	31,518
Consolidated VIE / SPE assets	32,021	31,518
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	117,358	113,641
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	117,358	113,641
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,052	1,582
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	48	43
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,100	1,625
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	67,704	60,851
Consolidated VIE / SPE assets	0	632
Significant unconsolidated VIE assets	67,704	60,219
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,294	2,479
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	0	5
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	3,294	2,484
Citi-administered asset-backed commercial paper conduits (ABCP)
Variable Interest Entity
Total involvement with SPE assets	19,621	14,018
Consolidated VIE / SPE assets	19,621	14,018
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	7,600	8,302
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	7,600	8,302
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,601	2,636
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	2,601	2,636
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	242,348	246,632
Consolidated VIE / SPE assets	9,672	11,085
Significant unconsolidated VIE assets	232,676	235,547
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	40,121	32,242
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	1,022	1,139
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	10,726	12,189
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	51,869	45,570
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	2,155	3,251
Consolidated VIE / SPE assets	672	905
Significant unconsolidated VIE assets	1,483	2,346
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2	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	1,108	1,498
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	1,110	1,500
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	22,167	20,597
Consolidated VIE / SPE assets	3	3
Significant unconsolidated VIE assets	22,164	20,594
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,731	2,512
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,143	3,617
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,420	3,562
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	9,294	9,691
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	482	904
Consolidated VIE / SPE assets	121	297
Significant unconsolidated VIE assets	361	607
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	58	75
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	13	224
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	71	299
Investment funds
Variable Interest Entity
Total involvement with SPE assets	534	498
Consolidated VIE / SPE assets	91	179
Significant unconsolidated VIE assets	443	319
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2	0
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	5	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	68	12
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	0	1
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	75	13
Other
Variable Interest Entity
Total involvement with SPE assets	0	0
Consolidated VIE / SPE assets	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