SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Variable Interest Entity
Total involvement with SPE assets	$ 452,854	$ 511,990
Consolidated VIE/SPE assets	61,996	62,201
Significant unconsolidated VIE assets	390,858	449,789
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	50,242	50,861
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,993	4,170
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	15,336	15,322
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	139	61
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	69,710	70,414
Private equity
Variable Interest Entity
Significant unconsolidated VIE assets	11,000	69,000
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	534	498
Venture capital investments
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	16,800	33,600
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	31,666	32,021
Consolidated VIE/SPE assets	31,666	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	125,515	117,358
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	125,515	117,358
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,093	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	138	48
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	2,231	2,100
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	66,721	67,704
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	66,721	67,704
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,191	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	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	3,191	3,294
Citi-administered asset-backed commercial paper conduits
Variable Interest Entity
Total involvement with SPE assets	18,600	19,621
Consolidated VIE/SPE assets	18,600	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	5,916	7,600
Consolidated VIE/SPE assets	0	0
Significant unconsolidated VIE assets	5,916	7,600
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,525	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	2,525	2,601
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	180,279	242,348
Consolidated VIE/SPE assets	10,931	9,672
Significant unconsolidated VIE assets	169,348	232,676
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	39,875	40,121
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	955	1,022
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	11,636	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	52,466	51,869
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	1,527	2,155
Consolidated VIE/SPE assets	596	672
Significant unconsolidated VIE assets	931	1,483
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	16	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	681	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	697	1,110
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	21,653	22,167
Consolidated VIE/SPE assets	3	3
Significant unconsolidated VIE assets	21,650	22,164
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,463	2,731
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,031	3,143
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,941	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	8,435	9,294
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	487	482
Consolidated VIE/SPE assets	97	121
Significant unconsolidated VIE assets	390	361
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	75	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	0	13
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	75	71
Investment funds
Variable Interest Entity
Total involvement with SPE assets	490	534
Consolidated VIE/SPE assets	103	91
Significant unconsolidated VIE assets	387	443
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	4	2
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	7	5
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	78	68
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	1	0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	$ 90	75
Other
Variable Interest Entity
Total involvement with SPE assets		0
Consolidated VIE/SPE assets		0
Significant unconsolidated VIE assets		0
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments		0
Maximum exposure to loss in significant unconsolidated VIEs, equity investments		0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments		0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives		0
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs		$ 0