CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues
Dividends from subsidiaries		$ 0	$ 0	$ 0	$ 0
Interest revenue		12,650	13,314	37,647	45,042
Interest revenue—intercompany		0	0	0	0
Interest expense		2,252	2,821	6,884	11,977
Interest expense—intercompany		0	0	0	0
Net interest revenue		10,398	10,493	30,763	33,065
Commissions and fees		3,399	2,753	10,443	8,707
Commissions and fees—intercompany		0	0	0	0
Principal transactions		2,233	2,508	8,450	11,926
Principal transactions—intercompany		0	0	0	0
Other revenue		1,124	1,548	4,299	4,101
Other revenue—intercompany		0	0	0	0
Total non-interest revenues		6,756	6,809	23,192	24,734
Total revenues, net of interest expense		17,154	17,302	53,955	57,799
Total provisions for credit losses and for benefits and claims	[1]	(192)	2,384	(3,313)	17,541
Operating expenses
Compensation and benefits		6,058	5,595	18,041	16,873
Compensation and benefits—intercompany		0	0	0	0
Other operating		5,426	5,369	15,708	15,194
Other operating—intercompany		0	0	0	0
Total operating expenses		11,484	10,964	33,749	32,067
Equity in undistributed income of subsidiaries		0	0	0	0
Income (loss) from continuing operations before income taxes		5,862	3,954	23,519	8,191
Provision (benefits) for income taxes		1,193	777	4,680	1,409
Income (loss) from continuing operations		4,669	3,177	18,839	6,782
Income (loss) from discontinued operations, net of taxes		(1)	(7)	7	(26)
Net income (loss) before attribution of noncontrolling interests		4,668	3,170	18,846	6,756
Noncontrolling interests		24	24	67	18
Citigroup’s net income		4,644	3,146	18,779	6,738
Comprehensive income
Add: Other comprehensive income (loss)	[2]	(1,731)	280	(4,793)	3,253
Total Citigroup comprehensive income (loss)		2,913	3,426	13,986	9,991
Add: Other comprehensive income (loss) attributable to noncontrolling interests		(31)	19	(71)	7
Add: Net income (loss) attributable to noncontrolling interests		24	24	67	18
Total comprehensive income (loss)		2,906	3,469	13,982	10,016
Reportable legal entities | Citigroup parent company
Revenues
Dividends from subsidiaries		2,592	2,250	6,392	2,355
Interest revenue		0	0	0	0
Interest revenue—intercompany		935	991	2,847	3,202
Interest expense		1,190	1,267	3,611	3,675
Interest expense—intercompany		56	61	234	451
Net interest revenue		(311)	(337)	(998)	(924)
Commissions and fees		0	0	0	0
Commissions and fees—intercompany		0	0	(27)	(19)
Principal transactions		130	(169)	1,007	(1,099)
Principal transactions—intercompany		(305)	42	(1,273)	606
Other revenue		(138)	(90)	(87)	(24)
Other revenue—intercompany		(44)	78	(105)	16
Total non-interest revenues		(357)	(139)	(485)	(520)
Total revenues, net of interest expense		1,924	1,774	4,909	911
Total provisions for credit losses and for benefits and claims		(2)	0	0	0
Operating expenses
Compensation and benefits		3	(21)	31	112
Compensation and benefits—intercompany		21	44	69	119
Other operating		35	5	60	37
Other operating—intercompany		2	4	8	12
Total operating expenses		61	32	168	280
Equity in undistributed income of subsidiaries		2,530	1,056	13,270	5,285
Income (loss) from continuing operations before income taxes		4,395	2,798	18,011	5,916
Provision (benefits) for income taxes		(249)	(348)	(768)	(822)
Income (loss) from continuing operations		4,644	3,146	18,779	6,738
Income (loss) from discontinued operations, net of taxes		0	0	0	0
Net income (loss) before attribution of noncontrolling interests		4,644	3,146	18,779	6,738
Noncontrolling interests		0	0	0	0
Citigroup’s net income		4,644	3,146	18,779	6,738
Comprehensive income
Add: Other comprehensive income (loss)		(1,731)	280	(4,793)	3,253
Total Citigroup comprehensive income (loss)		2,913	3,426	13,986	9,991
Add: Other comprehensive income (loss) attributable to noncontrolling interests		0	0	0	0
Add: Net income (loss) attributable to noncontrolling interests		0	0	0	0
Total comprehensive income (loss)		2,913	3,426	13,986	9,991
Reportable legal entities | CGMHI
Revenues
Dividends from subsidiaries		0	0	0	0
Interest revenue		844	1,128	2,829	4,340
Interest revenue—intercompany		129	153	410	776
Interest expense		201	274	645	1,795
Interest expense—intercompany		323	416	982	1,819
Net interest revenue		449	591	1,612	1,502
Commissions and fees		1,893	1,494	5,890	4,815
Commissions and fees—intercompany		85	30	220	267
Principal transactions		(1,468)	(3,779)	5,109	(518)
Principal transactions—intercompany		2,220	4,350	(2,128)	4,849
Other revenue		159	208	401	468
Other revenue—intercompany		(13)	12	(41)	38
Total non-interest revenues		2,876	2,315	9,451	9,919
Total revenues, net of interest expense		3,325	2,906	11,063	11,421
Total provisions for credit losses and for benefits and claims		2	(1)	9	(1)
Operating expenses
Compensation and benefits		1,347	1,165	3,984	3,806
Compensation and benefits—intercompany		0	0	0	0
Other operating		728	597	2,050	1,789
Other operating—intercompany		781	772	2,269	1,629
Total operating expenses		2,856	2,534	8,303	7,224
Equity in undistributed income of subsidiaries		0	0	0	0
Income (loss) from continuing operations before income taxes		467	373	2,751	4,198
Provision (benefits) for income taxes		183	165	516	1,217
Income (loss) from continuing operations		284	208	2,235	2,981
Income (loss) from discontinued operations, net of taxes		0	0	0	0
Net income (loss) before attribution of noncontrolling interests		284	208	2,235	2,981
Noncontrolling interests		0	0	0	0
Citigroup’s net income		284	208	2,235	2,981
Comprehensive income
Add: Other comprehensive income (loss)		(195)	(51)	(238)	277
Total Citigroup comprehensive income (loss)		89	157	1,997	3,258
Add: Other comprehensive income (loss) attributable to noncontrolling interests		0	0	0	0
Add: Net income (loss) attributable to noncontrolling interests		0	0	0	0
Total comprehensive income (loss)		89	157	1,997	3,258
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Revenues
Dividends from subsidiaries		0	0	0	0
Interest revenue		11,806	12,186	34,818	40,702
Interest revenue—intercompany		(1,064)	(1,144)	(3,257)	(3,978)
Interest expense		861	1,280	2,628	6,507
Interest expense—intercompany		(379)	(477)	(1,216)	(2,270)
Net interest revenue		10,260	10,239	30,149	32,487
Commissions and fees		1,506	1,259	4,553	3,892
Commissions and fees—intercompany		(85)	(30)	(193)	(248)
Principal transactions		3,571	6,456	2,334	13,543
Principal transactions—intercompany		(1,915)	(4,392)	3,401	(5,455)
Other revenue		1,103	1,430	3,985	3,657
Other revenue—intercompany		57	(90)	146	(54)
Total non-interest revenues		4,237	4,633	14,226	15,335
Total revenues, net of interest expense		14,497	14,872	44,375	47,822
Total provisions for credit losses and for benefits and claims		(192)	2,385	(3,322)	17,542
Operating expenses
Compensation and benefits		4,708	4,451	14,026	12,955
Compensation and benefits—intercompany		(21)	(44)	(69)	(119)
Other operating		4,663	4,767	13,598	13,368
Other operating—intercompany		(783)	(776)	(2,277)	(1,641)
Total operating expenses		8,567	8,398	25,278	24,563
Equity in undistributed income of subsidiaries		0	0	0	0
Income (loss) from continuing operations before income taxes		6,122	4,089	22,419	5,717
Provision (benefits) for income taxes		1,259	960	4,932	1,014
Income (loss) from continuing operations		4,863	3,129	17,487	4,703
Income (loss) from discontinued operations, net of taxes		(1)	(7)	7	(26)
Net income (loss) before attribution of noncontrolling interests		4,862	3,122	17,494	4,677
Noncontrolling interests		24	24	67	18
Citigroup’s net income		4,838	3,098	17,427	4,659
Comprehensive income
Add: Other comprehensive income (loss)		2,007	(2,178)	578	10,058
Total Citigroup comprehensive income (loss)		6,845	920	18,005	14,717
Add: Other comprehensive income (loss) attributable to noncontrolling interests		(31)	19	(71)	7
Add: Net income (loss) attributable to noncontrolling interests		24	24	67	18
Total comprehensive income (loss)		6,838	963	18,001	14,742
Consolidating adjustments
Revenues
Dividends from subsidiaries		(2,592)	(2,250)	(6,392)	(2,355)
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 revenue		0	0	0	0
Other revenue—intercompany		0	0	0	0
Total non-interest revenues		0	0	0	0
Total revenues, net of interest expense		(2,592)	(2,250)	(6,392)	(2,355)
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		(2,530)	(1,056)	(13,270)	(5,285)
Income (loss) from continuing operations before income taxes		(5,122)	(3,306)	(19,662)	(7,640)
Provision (benefits) for income taxes		0	0	0	0
Income (loss) from continuing operations		(5,122)	(3,306)	(19,662)	(7,640)
Income (loss) from discontinued operations, net of taxes		0	0	0	0
Net income (loss) before attribution of noncontrolling interests		(5,122)	(3,306)	(19,662)	(7,640)
Noncontrolling interests		0	0	0	0
Citigroup’s net income		(5,122)	(3,306)	(19,662)	(7,640)
Comprehensive income
Add: Other comprehensive income (loss)		(1,812)	2,229	(340)	(10,335)
Total Citigroup comprehensive income (loss)		(6,934)	(1,077)	(20,002)	(17,975)
Add: Other comprehensive income (loss) attributable to noncontrolling interests		0	0	0	0
Add: Net income (loss) attributable to noncontrolling interests		0	0	0	0
Total comprehensive income (loss)		$ (6,934)	$ (1,077)	$ (20,002)	$ (17,975)

[1] This total excludes the provision for credit losses on AFS securities, which is disclosed separately above.

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