CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues
Dividends from subsidiaries	$ 0	$ 0	$ 0	$ 0
Interest revenue	19,712	17,550	38,788	33,882
Interest revenue—intercompany	0	0	0	0
Interest expense	7,762	5,885	15,079	11,045
Interest expense—intercompany	0	0	0	0
Net interest revenue	11,950	11,665	23,709	22,837
Commissions and fees	2,881	3,111	5,807	6,141
Commissions and fees—intercompany	0	0	0	0
Principal transactions	1,874	2,126	4,678	5,368
Principal transactions—intercompany	0	0	0	0
Other income	2,053	1,567	3,140	2,995
Other income—intercompany	0	0	0	0
Total non-interest revenues	6,808	6,804	13,625	14,504
Total revenues, net of interest expense	18,758	18,469	37,334	37,341
Provisions for credit losses and for benefits and claims	2,093	1,812	4,073	3,669
Operating expenses
Compensation and benefits	5,381	5,452	11,039	11,259
Compensation and benefits—intercompany	0	0	0	0
Other operating	5,119	5,260	10,045	10,378
Other operating—intercompany	0	0	0	0
Total operating expenses	10,500	10,712	21,084	21,637
Equity in undistributed income of subsidiaries	0	0	0	0
Income (loss) from continuing operations before income taxes	6,165	5,945	12,177	12,035
Provision for income taxes	1,373	1,444	2,648	2,885
Income from continuing operations	4,792	4,501	9,529	9,150
Loss from discontinued operations, net of taxes	17	15	15	8
Net income before attribution of noncontrolling interests	4,809	4,516	9,544	9,158
Noncontrolling interests	10	26	35	48
Citigroup’s net income	4,799	4,490	9,509	9,110
Comprehensive income
Add: Other comprehensive income (loss)	1,105	(2,875)	1,967	(2,823)
Citigroup’s total comprehensive income	5,904	1,615	11,476	6,287
Add: Other comprehensive income (loss) attributable to noncontrolling interests	20	(57)	7	(43)
Add: Net income attributable to noncontrolling interests	10	26	35	48
Total comprehensive income (loss)	5,934	1,584	11,518	6,292
Reportable legal entities | Citigroup parent company
Revenues
Dividends from subsidiaries	5,049	3,115	14,216	8,700
Interest revenue	0	14	0	66
Interest revenue—intercompany	1,327	1,225	2,652	2,355
Interest expense	1,278	813	2,549	2,051
Interest expense—intercompany	202	716	514	975
Net interest revenue	(153)	(290)	(411)	(605)
Commissions and fees	0	0	0	0
Commissions and fees—intercompany	0	(1)	(1)	(1)
Principal transactions	(565)	(1,206)	(1,390)	(175)
Principal transactions—intercompany	791	(472)	1,238	(858)
Other income	(368)	1,480	(49)	552
Other income—intercompany	9	(121)	(25)	(66)
Total non-interest revenues	(133)	(320)	(227)	(548)
Total revenues, net of interest expense	4,763	2,505	13,578	7,547
Provisions for credit losses and for benefits and claims	0	0	0	0
Operating expenses
Compensation and benefits	4	1	37	135
Compensation and benefits—intercompany	17	29	43	63
Other operating	9	(52)	14	(9)
Other operating—intercompany	5	13	10	25
Total operating expenses	35	(9)	104	214
Equity in undistributed income of subsidiaries	(146)	1,485	(4,349)	1,039
Income (loss) from continuing operations before income taxes	4,582	3,999	9,125	8,372
Provision for income taxes	(217)	(491)	(384)	(738)
Income from continuing operations	4,799	4,490	9,509	9,110
Loss from discontinued operations, net of taxes	0	0	0	0
Net income before attribution of noncontrolling interests	4,799	4,490	9,509	9,110
Noncontrolling interests	0	0	0	0
Citigroup’s net income	4,799	4,490	9,509	9,110
Comprehensive income
Add: Other comprehensive income (loss)	1,105	(2,875)	1,967	(2,823)
Citigroup’s total comprehensive income	5,904	1,615	11,476	6,287
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0	0	0
Add: Net income attributable to noncontrolling interests	0	0	0	0
Total comprehensive income (loss)	5,904	1,615	11,476	6,287
Reportable legal entities | CGMHI
Revenues
Dividends from subsidiaries	0	0	0	0
Interest revenue	3,184	2,398	5,756	4,053
Interest revenue—intercompany	518	399	1,021	782
Interest expense	1,911	1,314	3,735	2,327
Interest expense—intercompany	1,152	896	2,227	1,668
Net interest revenue	639	587	815	840
Commissions and fees	1,309	1,347	2,616	2,599
Commissions and fees—intercompany	94	91	215	91
Principal transactions	1,142	(697)	108	224
Principal transactions—intercompany	(675)	1,279	1,361	1,471
Other income	498	188	597	341
Other income—intercompany	14	(19)	56	31
Total non-interest revenues	2,382	2,189	4,953	4,757
Total revenues, net of interest expense	3,021	2,776	5,768	5,597
Provisions for credit losses and for benefits and claims	0	(24)	0	(24)
Operating expenses
Compensation and benefits	1,166	1,282	2,450	2,547
Compensation and benefits—intercompany	0	0	0	0
Other operating	540	578	1,093	1,126
Other operating—intercompany	582	693	1,164	1,271
Total operating expenses	2,288	2,553	4,707	4,944
Equity in undistributed income of subsidiaries	0	0	0	0
Income (loss) from continuing operations before income taxes	733	247	1,061	677
Provision for income taxes	8	619	148	684
Income from continuing operations	725	(372)	913	(7)
Loss from discontinued operations, net of taxes	0	0	0	0
Net income before attribution of noncontrolling interests	725	(372)	913	(7)
Noncontrolling interests	0	0	0	0
Citigroup’s net income	725	(372)	913	(7)
Comprehensive income
Add: Other comprehensive income (loss)	(12)	(72)	(301)	10
Citigroup’s total comprehensive income	713	(444)	612	3
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0	0	0
Add: Net income attributable to noncontrolling interests	0	0	0	0
Total comprehensive income (loss)	713	(444)	612	3
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Revenues
Dividends from subsidiaries	0	0	0	0
Interest revenue	16,528	15,138	33,032	29,763
Interest revenue—intercompany	(1,845)	(1,624)	(3,673)	(3,137)
Interest expense	4,573	3,758	8,795	6,667
Interest expense—intercompany	(1,354)	(1,612)	(2,741)	(2,643)
Net interest revenue	11,464	11,368	23,305	22,602
Commissions and fees	1,572	1,764	3,191	3,542
Commissions and fees—intercompany	(94)	(90)	(214)	(90)
Principal transactions	1,297	4,029	5,960	5,319
Principal transactions—intercompany	(116)	(807)	(2,599)	(613)
Other income	1,923	(101)	2,592	2,102
Other income—intercompany	(23)	140	(31)	35
Total non-interest revenues	4,559	4,935	8,899	10,295
Total revenues, net of interest expense	16,023	16,303	32,204	32,897
Provisions for credit losses and for benefits and claims	2,093	1,836	4,073	3,693
Operating expenses
Compensation and benefits	4,211	4,169	8,552	8,577
Compensation and benefits—intercompany	(17)	(29)	(43)	(63)
Other operating	4,570	4,734	8,938	9,261
Other operating—intercompany	(587)	(706)	(1,174)	(1,296)
Total operating expenses	8,177	8,168	16,273	16,479
Equity in undistributed income of subsidiaries	0	0	0	0
Income (loss) from continuing operations before income taxes	5,753	6,299	11,858	12,725
Provision for income taxes	1,582	1,316	2,884	2,939
Income from continuing operations	4,171	4,983	8,974	9,786
Loss from discontinued operations, net of taxes	17	15	15	8
Net income before attribution of noncontrolling interests	4,188	4,998	8,989	9,794
Noncontrolling interests	10	26	35	48
Citigroup’s net income	4,178	4,972	8,954	9,746
Comprehensive income
Add: Other comprehensive income (loss)	734	5,401	1,733	2,245
Citigroup’s total comprehensive income	4,912	10,373	10,687	11,991
Add: Other comprehensive income (loss) attributable to noncontrolling interests	20	(57)	7	(43)
Add: Net income attributable to noncontrolling interests	10	26	35	48
Total comprehensive income (loss)	4,942	10,342	10,729	11,996
Consolidating adjustments
Revenues
Dividends from subsidiaries	(5,049)	(3,115)	(14,216)	(8,700)
Interest revenue	0	0	0	0
Interest revenue—intercompany	0	0	0	0
Interest expense	0	0	0	0
Interest expense—intercompany	0	0	0	0
Net interest revenue	0	0	0	0
Commissions and fees	0	0	0	0
Commissions and fees—intercompany	0	0	0	0
Principal transactions	0	0	0	0
Principal transactions—intercompany	0	0	0	0
Other income	0	0	0	0
Other income—intercompany	0	0	0	0
Total non-interest revenues	0	0	0	0
Total revenues, net of interest expense	(5,049)	(3,115)	(14,216)	(8,700)
Provisions for credit losses and for benefits and claims	0	0	0	0
Operating expenses
Compensation and benefits	0	0	0	0
Compensation and benefits—intercompany	0	0	0	0
Other operating	0	0	0	0
Other operating—intercompany	0	0	0	0
Total operating expenses	0	0	0	0
Equity in undistributed income of subsidiaries	146	(1,485)	4,349	(1,039)
Income (loss) from continuing operations before income taxes	(4,903)	(4,600)	(9,867)	(9,739)
Provision for income taxes	0	0	0	0
Income from continuing operations	(4,903)	(4,600)	(9,867)	(9,739)
Loss from discontinued operations, net of taxes	0	0	0	0
Net income before attribution of noncontrolling interests	(4,903)	(4,600)	(9,867)	(9,739)
Noncontrolling interests	0	0	0	0
Citigroup’s net income	(4,903)	(4,600)	(9,867)	(9,739)
Comprehensive income
Add: Other comprehensive income (loss)	(722)	(5,329)	(1,432)	(2,255)
Citigroup’s total comprehensive income	(5,625)	(9,929)	(11,299)	(11,994)
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0	0	0
Add: Net income attributable to noncontrolling interests	0	0	0	0
Total comprehensive income (loss)	$ (5,625)	$ (9,929)	$ (11,299)	$ (11,994)