CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues
Dividends from subsidiaries		$ 0	$ 0	$ 0	$ 0
Interest revenue		14,589	19,712	31,728	38,788
Interest revenue—intercompany		0	0	0	0
Interest expense		3,509	7,762	9,156	15,079
Interest expense—intercompany		0	0	0	0
Net interest revenue		11,080	11,950	22,572	23,709
Commissions and fees		2,933	2,881	5,954	5,807
Commissions and fees—intercompany		0	0	0	0
Principal transactions		4,157	1,874	9,418	4,678
Principal transactions—intercompany		0	0	0	0
Other income		1,596	2,053	2,553	3,140
Other income—intercompany		0	0	0	0
Total non-interest revenues		8,686	6,808	17,925	13,625
Total revenues, net of interest expense		19,766	18,758	40,497	37,334
Total provisions for credit losses and for benefits and claims		7,903	2,093	14,930	4,073
Operating expenses
Compensation and benefits		5,624	5,381	11,278	11,039
Compensation and benefits—intercompany		0	0	0	0
Other operating		4,791	5,119	9,731	10,045
Other operating—intercompany		0	0	0	0
Total operating expenses		10,415	10,500	21,009	21,084
Equity in undistributed income of subsidiaries		0	0	0	0
Income (loss) from continuing operations before income taxes		1,448	6,165	4,558	12,177
Provision for income taxes		131	1,373	707	2,648
Income from continuing operations		1,317	4,792	3,851	9,529
Loss from discontinued operations, net of taxes		(1)	17	(19)	15
Net income before attribution of noncontrolling interests		1,316	4,809	3,832	9,544
Noncontrolling interests		0	10	(6)	35
Citigroup’s net income		1,316	4,799	3,838	9,509
Comprehensive income
Add: Other comprehensive income (loss)	[1]	(824)	1,105	2,973	1,967
Citigroup’s total comprehensive income		492	5,904	6,811	11,476
Add: Other comprehensive income (loss) attributable to noncontrolling interests		39	20	(12)	7
Add: Net income attributable to noncontrolling interests		0	10	(6)	35
Total comprehensive income (loss)		531	5,934	6,793	11,518
Reportable legal entities | Citigroup parent company
Revenues
Dividends from subsidiaries		0	5,049	105	14,216
Interest revenue		0	0	0	0
Interest revenue—intercompany		1,067	1,327	2,211	2,652
Interest expense		1,265	1,278	2,408	2,549
Interest expense—intercompany		142	202	390	514
Net interest revenue		(340)	(153)	(587)	(411)
Commissions and fees		0	0	0	0
Commissions and fees—intercompany		0	0	(19)	(1)
Principal transactions		(258)	(565)	(930)	(1,390)
Principal transactions—intercompany		62	791	564	1,238
Other income		(14)	(368)	66	(49)
Other income—intercompany		8	9	(62)	(25)
Total non-interest revenues		(202)	(133)	(381)	(227)
Total revenues, net of interest expense		(542)	4,763	(863)	13,578
Total provisions for credit losses and for benefits and claims		0	0	0	0
Operating expenses
Compensation and benefits		105	4	133	37
Compensation and benefits—intercompany		1	17	75	43
Other operating		9	9	32	14
Other operating—intercompany		4	5	8	10
Total operating expenses		119	35	248	104
Equity in undistributed income of subsidiaries		2,107	(146)	4,475	(4,349)
Income (loss) from continuing operations before income taxes		1,446	4,582	3,364	9,125
Provision for income taxes		130	(217)	(474)	(384)
Income from continuing operations		1,316	4,799	3,838	9,509
Loss from discontinued operations, net of taxes		0	0	0	0
Net income before attribution of noncontrolling interests		1,316	4,799	3,838	9,509
Noncontrolling interests		0	0	0	0
Citigroup’s net income		1,316	4,799	3,838	9,509
Comprehensive income
Add: Other comprehensive income (loss)		(824)	1,105	2,973	1,967
Citigroup’s total comprehensive income		492	5,904	6,811	11,476
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)		492	5,904	6,811	11,476
Reportable legal entities | CGMHI
Revenues
Dividends from subsidiaries		0	0	0	0
Interest revenue		1,309	3,184	3,212	5,756
Interest revenue—intercompany		282	518	623	1,021
Interest expense		380	1,911	1,521	3,735
Interest expense—intercompany		621	1,152	1,403	2,227
Net interest revenue		590	639	911	815
Commissions and fees		1,771	1,309	3,321	2,616
Commissions and fees—intercompany		73	94	237	215
Principal transactions		(2,993)	1,142	3,261	108
Principal transactions—intercompany		4,890	(675)	499	1,361
Other income		211	498	260	597
Other income—intercompany		13	14	26	56
Total non-interest revenues		3,965	2,382	7,604	4,953
Total revenues, net of interest expense		4,555	3,021	8,515	5,768
Total provisions for credit losses and for benefits and claims		1	0	0	0
Operating expenses
Compensation and benefits		1,345	1,166	2,641	2,450
Compensation and benefits—intercompany		0	0	0	0
Other operating		594	540	1,192	1,093
Other operating—intercompany		375	582	857	1,164
Total operating expenses		2,314	2,288	4,690	4,707
Equity in undistributed income of subsidiaries		0	0	0	0
Income (loss) from continuing operations before income taxes		2,240	733	3,825	1,061
Provision for income taxes		715	8	1,052	148
Income from continuing operations		1,525	725	2,773	913
Loss from discontinued operations, net of taxes		0	0	0	0
Net income before attribution of noncontrolling interests		1,525	725	2,773	913
Noncontrolling interests		0	0	0	0
Citigroup’s net income		1,525	725	2,773	913
Comprehensive income
Add: Other comprehensive income (loss)		(1,429)	(12)	328	(301)
Citigroup’s total comprehensive income		96	713	3,101	612
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)		96	713	3,101	612
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Revenues
Dividends from subsidiaries		0	0	0	0
Interest revenue		13,280	16,528	28,516	33,032
Interest revenue—intercompany		(1,349)	(1,845)	(2,834)	(3,673)
Interest expense		1,864	4,573	5,227	8,795
Interest expense—intercompany		(763)	(1,354)	(1,793)	(2,741)
Net interest revenue		10,830	11,464	22,248	23,305
Commissions and fees		1,162	1,572	2,633	3,191
Commissions and fees—intercompany		(73)	(94)	(218)	(214)
Principal transactions		7,408	1,297	7,087	5,960
Principal transactions—intercompany		(4,952)	(116)	(1,063)	(2,599)
Other income		1,399	1,923	2,227	2,592
Other income—intercompany		(21)	(23)	36	(31)
Total non-interest revenues		4,923	4,559	10,702	8,899
Total revenues, net of interest expense		15,753	16,023	32,950	32,204
Total provisions for credit losses and for benefits and claims		7,902	2,093	14,930	4,073
Operating expenses
Compensation and benefits		4,174	4,211	8,504	8,552
Compensation and benefits—intercompany		(1)	(17)	(75)	(43)
Other operating		4,188	4,570	8,507	8,938
Other operating—intercompany		(379)	(587)	(865)	(1,174)
Total operating expenses		7,982	8,177	16,071	16,273
Equity in undistributed income of subsidiaries		0	0	0	0
Income (loss) from continuing operations before income taxes		(131)	5,753	1,949	11,858
Provision for income taxes		(714)	1,582	129	2,884
Income from continuing operations		583	4,171	1,820	8,974
Loss from discontinued operations, net of taxes		(1)	17	(19)	15
Net income before attribution of noncontrolling interests		582	4,188	1,801	8,989
Noncontrolling interests		0	10	(6)	35
Citigroup’s net income		582	4,178	1,807	8,954
Comprehensive income
Add: Other comprehensive income (loss)		(1,223)	734	12,236	1,733
Citigroup’s total comprehensive income		(641)	4,912	14,043	10,687
Add: Other comprehensive income (loss) attributable to noncontrolling interests		39	20	(12)	7
Add: Net income attributable to noncontrolling interests		0	10	(6)	35
Total comprehensive income (loss)		(602)	4,942	14,025	10,729
Consolidating adjustments
Revenues
Dividends from subsidiaries		0	(5,049)	(105)	(14,216)
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		0	(5,049)	(105)	(14,216)
Total 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		(2,107)	146	(4,475)	4,349
Income (loss) from continuing operations before income taxes		(2,107)	(4,903)	(4,580)	(9,867)
Provision for income taxes		0	0	0	0
Income from continuing operations		(2,107)	(4,903)	(4,580)	(9,867)
Loss from discontinued operations, net of taxes		0	0	0	0
Net income before attribution of noncontrolling interests		(2,107)	(4,903)	(4,580)	(9,867)
Noncontrolling interests		0	0	0	0
Citigroup’s net income		(2,107)	(4,903)	(4,580)	(9,867)
Comprehensive income
Add: Other comprehensive income (loss)		2,652	(722)	(12,564)	(1,432)
Citigroup’s total comprehensive income		545	(5,625)	(17,144)	(11,299)
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)		$ 545	$ (5,625)	$ (17,144)	$ (11,299)

[1] See Note 17 to the Consolidated Financial Statements.