SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Variable Interest Entity
Total involvement with SPE assets	$ 448,026	$ 511,990
Consolidated VIE/SPE assets	60,897	62,201
Significant unconsolidated VIE assets	387,129	449,789
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	51,396	50,861
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	4,021	4,170
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	14,397	15,322
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	120	61
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	69,934	70,414
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	10,000	69,000
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	252	498
Venture capital investments
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	25,200	33,600
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	30,241	32,021
Consolidated VIE/SPE assets	30,241	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 securitizations - U.S. agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	124,641	117,358
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	124,641	117,358
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,059	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	107	48
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,166	2,100
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	63,156	67,704
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	63,156	67,704
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,264	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	7	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	3,271	3,294
Citi-administered asset-backed commercial paper conduits
Variable Interest Entity
Total involvement with SPE assets	19,419	19,621
Consolidated VIE/SPE assets	19,419	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	7,134	7,600
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	7,134	7,600
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,599	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	2,599	2,601
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	178,461	242,348
Consolidated VIE/SPE assets	10,336	9,672
Significant unconsolidated VIE assets	168,125	232,676
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	40,737	40,121
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	990	1,022
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	10,261	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	51,988	51,869
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	1,885	2,155
Consolidated VIE/SPE assets	673	672
Significant unconsolidated VIE assets	1,212	1,483
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	35	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	867	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	902	1,110
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	22,107	22,167
Consolidated VIE/SPE assets	3	3
Significant unconsolidated VIE assets	22,104	22,164
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,641	2,731
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,025	3,143
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,196	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	8,862	9,294
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	490	482
Consolidated VIE/SPE assets	129	121
Significant unconsolidated VIE assets	361	361
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	58	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	13	13
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	71	71
Investment funds
Variable Interest Entity
Total involvement with SPE assets	492	534
Consolidated VIE/SPE assets	96	91
Significant unconsolidated VIE assets	396	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	6	5
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	66	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	75	75
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