SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Variable Interest Entity
Total involvement with SPE assets	$ 488,417	$ 500,212
Consolidated VIE/SPE assets	56,726	58,637
Significant unconsolidated VIE assets	431,691	441,575
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	46,604	41,528
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	4,307	4,756
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	16,653	17,266
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	62	268
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	67,626	63,818
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	75,000	100,000
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	500	497
Venture capital investments
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	43,400	55,600
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	31,139	31,518
Consolidated VIE/SPE assets	31,139	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 securitizations - U.S. agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	112,923	113,641
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	112,923	113,641
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,019	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	49	43
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,068	1,625
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	59,730	60,851
Consolidated VIE/SPE assets	0	632
Significant unconsolidated VIE assets	59,730	60,219
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,606	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	7	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	2,613	2,484
Citi-administered asset-backed commercial paper conduits
Variable Interest Entity
Total involvement with SPE assets	15,583	14,018
Consolidated VIE/SPE assets	15,583	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	7,563	8,302
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	7,563	8,302
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,580	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	2,580	2,636
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	236,093	246,632
Consolidated VIE/SPE assets	8,929	11,085
Significant unconsolidated VIE assets	227,164	235,547
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	36,588	32,242
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	1,050	1,139
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	11,421	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	49,059	45,570
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	2,521	3,251
Consolidated VIE/SPE assets	665	905
Significant unconsolidated VIE assets	1,856	2,346
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	10	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	1,395	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	1,405	1,500
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	21,677	20,597
Consolidated VIE/SPE assets	3	3
Significant unconsolidated VIE assets	21,674	20,594
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,738	2,512
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,252	3,617
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,810	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	9,800	9,691
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	696	904
Consolidated VIE/SPE assets	325	297
Significant unconsolidated VIE assets	371	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	492	498
Consolidated VIE/SPE assets	82	179
Significant unconsolidated VIE assets	410	319
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	5	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	20	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	30	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