SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Variable Interest Entity
Total involvement with SPE assets	$ 432,574	$ 418,045
Consolidated VIE / SPE assets	81,037	84,794
Significant unconsolidated VIE assets	351,537	333,251
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	30,444	31,070
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,905	3,448
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	9,508	9,153
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	677	670
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	44,534	44,341
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	51,365	54,916
Consolidated VIE / SPE assets	51,365	54,916
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	232,273	217,291
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	232,273	217,291
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	4,541	3,571
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	91	95
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	4,632	3,666
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	20,368	13,036
Consolidated VIE / SPE assets	1,540	1,586
Significant unconsolidated VIE assets	18,828	11,450
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	425	527
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	35	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	1	1
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	461	528
Citi-administered asset-backed commercial paper conduits (ABCP)
Variable Interest Entity
Total involvement with SPE assets	21,437	21,280
Consolidated VIE / SPE assets	21,437	21,280
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	15,071	16,719
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	15,071	16,719
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,502	3,150
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	84	86
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	3,586	3,236
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	56,719	58,862
Consolidated VIE / SPE assets	1,263	1,364
Significant unconsolidated VIE assets	55,456	57,498
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	19,211	21,270
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	406	269
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,998	3,616
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	451	436
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	24,066	25,591
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	8,167	8,572
Consolidated VIE / SPE assets	3,574	3,830
Significant unconsolidated VIE assets	4,593	4,742
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	50	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	2,962	3,100
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	3,012	3,102
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	19,274	20,290
Consolidated VIE / SPE assets	42	44
Significant unconsolidated VIE assets	19,232	20,246
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,339	2,196
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	2,757	2,487
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,399	2,335
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	7,495	7,018
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	502	434
Consolidated VIE / SPE assets	352	335
Significant unconsolidated VIE assets	150	99
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	50	49
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	50	49
Investment funds
Variable Interest Entity
Total involvement with SPE assets	2,533	1,730
Consolidated VIE / SPE assets	828	842
Significant unconsolidated VIE assets	1,705	888
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	25	13
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	157	138
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	78	102
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	260	253
Other
Variable Interest Entity
Total involvement with SPE assets	4,865	4,915
Consolidated VIE / SPE assets	636	597
Significant unconsolidated VIE assets	4,229	4,318
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	301	292
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	550	554
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	71	0
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	50	52
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	972	898
Mortgage-backed securities
Funded and Unfunded Exposure
Private label mortgage-backed securities, outstanding	11,000	12,000
Citicorp
Variable Interest Entity
Total involvement with SPE assets	$ 402,200	$ 383,200