SECURITIZATIONS AND VARIABLE INTEREST ENTITIES - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Variable Interest Entity
Total involvement with SPE assets	$ 516,610	$ 536,710
Consolidated VIE / SPE assets	96,321	102,790
Significant unconsolidated VIE assets	420,289	433,920
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	34,068	32,909
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	3,279	4,102
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	8,397	8,313
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	596	613
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	46,340	45,937
Credit card securitizations
Variable Interest Entity
Total involvement with SPE assets	55,415	60,503
Consolidated VIE / SPE assets	55,242	60,271
Significant unconsolidated VIE assets	173	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	248,073	264,848
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	248,073	264,848
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	3,983	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	102	110
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	4,085	5,323
Mortgage securitizations - Non-agency-sponsored
Variable Interest Entity
Total involvement with SPE assets	15,878	17,888
Consolidated VIE / SPE assets	1,010	1,304
Significant unconsolidated VIE assets	14,868	16,584
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	459	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	460	578
Citi-administered asset-backed commercial paper conduits (ABCP)
Variable Interest Entity
Total involvement with SPE assets	25,931	29,181
Consolidated VIE / SPE assets	25,931	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	4,589	5,617
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	4,589	5,617
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	362	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	84	86
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	446	305
Collateralized loan obligations (CLOs)
Variable Interest Entity
Total involvement with SPE assets	19,136	14,119
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	19,136	14,119
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,172	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	2,172	1,746
Asset-based financing
Variable Interest Entity
Total involvement with SPE assets	67,913	63,900
Consolidated VIE / SPE assets	1,178	1,151
Significant unconsolidated VIE assets	66,735	62,749
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	24,815	22,928
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	169	66
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,148	2,271
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	354	333
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	27,486	25,598
Municipal securities tender option bond trusts (TOBs)
Variable Interest Entity
Total involvement with SPE assets	10,496	12,280
Consolidated VIE / SPE assets	5,236	6,671
Significant unconsolidated VIE assets	5,260	5,609
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	85	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	3,440	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	3,525	3,673
Municipal investments
Variable Interest Entity
Total involvement with SPE assets	22,418	23,706
Consolidated VIE / SPE assets	57	70
Significant unconsolidated VIE assets	22,361	23,636
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	2,084	2,014
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	2,154	2,197
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	2,660	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	6,898	6,436
Client intermediation
Variable Interest Entity
Total involvement with SPE assets	2,225	1,745
Consolidated VIE / SPE assets	695	137
Significant unconsolidated VIE assets	1,530	1,608
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	22	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	22	20
Investment funds
Variable Interest Entity
Total involvement with SPE assets	31,714	31,992
Consolidated VIE / SPE assets	943	1,096
Significant unconsolidated VIE assets	30,771	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	374	382
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	102	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	489	522
Trust preferred securities
Variable Interest Entity
Total involvement with SPE assets	2,635	2,633
Consolidated VIE / SPE assets	0	0
Significant unconsolidated VIE assets	2,635	2,633
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	0	0
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	6	6
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	6	6
Other
Variable Interest Entity
Total involvement with SPE assets	10,187	8,298
Consolidated VIE / SPE assets	6,029	2,909
Significant unconsolidated VIE assets	4,158	5,389
Funded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, debt investments	73	183
Maximum exposure to loss in significant unconsolidated VIEs, equity investments	576	1,451
Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs, funding commitments	47	23
Maximum exposure to loss in significant unconsolidated VIEs, guarantees and derivatives	55	73
Funded and Unfunded Exposure
Maximum exposure to loss in significant unconsolidated VIEs	751	1,730
Mortgage-backed securities
Funded and Unfunded Exposure
Private label mortgage-backed securities, outstanding	13,000	14,000
Citicorp
Variable Interest Entity
Total involvement with SPE assets	$ 470,200	$ 483,900