SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Variable Interest Entity
Total involvement with SPE assets	$ 497,929	$ 534,077
Consolidated VIE / SPE assets	95,756	102,790
Significant unconsolidated VIE assets	402,173	431,287
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	33,595	32,909
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,381	4,096
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	9,179	8,313
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	636	613
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	46,791	45,931
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	54,075	60,503
Consolidated VIE / SPE assets	53,924	60,271
Significant unconsolidated VIE assets	151	232
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	238,077	264,848
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	238,077	264,848
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,840	5,213
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	97	110
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	3,937	5,323
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	16,061	17,888
Consolidated VIE / SPE assets	1,728	1,304
Significant unconsolidated VIE assets	14,333	16,584
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	458	577
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	1	1
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	459	578
Citi-administered asset-backed commercial paper conduits (ABCP)
Variable Interest Entity
Total involvement with SPE assets	24,117	29,181
Consolidated VIE / SPE assets	24,117	29,181
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 debt obligations (CDOs)
Variable Interest Entity
Total involvement with SPE assets	3,515	5,617
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	3,515	5,617
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	165	219
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	86	86
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	251	305
Collateralized loan obligations (CLOs)
Variable Interest Entity
Total involvement with SPE assets	16,567	14,119
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	16,567	14,119
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,484	1,746
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	2,484	1,746
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	71,046	63,900
Consolidated VIE / SPE assets	1,335	1,151
Significant unconsolidated VIE assets	69,711	62,749
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	24,183	22,928
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	267	66
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,266	2,271
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	399	333
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	28,115	25,598
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	9,087	12,280
Consolidated VIE / SPE assets	4,259	6,671
Significant unconsolidated VIE assets	4,828	5,609
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	56	3
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	0	0
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	3,136	3,670
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	3,192	3,673
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	22,512	23,706
Consolidated VIE / SPE assets	54	70
Significant unconsolidated VIE assets	22,458	23,636
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,272	2,014
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	2,208	2,197
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,651	2,225
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	7,131	6,436
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	1,800	1,745
Consolidated VIE / SPE assets	358	137
Significant unconsolidated VIE assets	1,442	1,608
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	49	10
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	10
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	49	20
Investment funds
Variable Interest Entity
Total involvement with SPE assets	27,801	31,992
Consolidated VIE / SPE assets	918	1,096
Significant unconsolidated VIE assets	26,883	30,896
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	13	16
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	350	382
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	104	124
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	467	522
Other
Variable Interest Entity
Total involvement with SPE assets	13,271	8,298
Consolidated VIE / SPE assets	9,063	2,909
Significant unconsolidated VIE assets	4,208	5,389
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	75	183
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	556	1,451
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	22	23
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	53	73
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	706	1,730
Mortgage-backed securities
Funded and Unfunded Exposure
Private label mortgage-backed securities, outstanding	12,000	14,000
Citicorp
Variable Interest Entity
Total involvement with SPE assets	$ 451,700	$ 481,300