CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues
Dividends from subsidiaries	$ 0	$ 0	$ 0	$ 0
Interest revenue	15,201	14,356	29,624	28,523
Interest revenue—intercompany	0	0	0	0
Interest expense	4,036	3,120	7,602	6,060
Interest expense—intercompany	0	0	0	0
Net interest revenue	11,165	11,236	22,022	22,463
Commissions and fees	2,937	2,725	5,696	5,188
Commissions and fees—intercompany	0	0	0	0
Principal transactions	2,562	1,816	5,584	3,656
Principal transactions—intercompany	0	0	0	0
Other income	1,237	1,771	2,719	3,796
Other income—intercompany	0	0	0	0
Total non-interest revenues	6,736	6,312	13,999	12,640
Total revenues, net of interest expense	17,901	17,548	36,021	35,103
Provisions for credit losses and for benefits and claims	1,717	1,409	3,379	3,454
Operating expenses
Compensation and benefits	5,463	5,229	10,997	10,785
Compensation and benefits—intercompany	0	0	0	0
Other operating	5,043	5,140	9,986	10,107
Other operating—intercompany	0	0	0	0
Total operating expenses	10,506	10,369	20,983	20,892
Equity in undistributed income of subsidiaries	0	0	0	0
Income (loss) from continuing operations before income taxes	5,678	5,770	11,659	10,757
Provision for income taxes	1,795	1,723	3,658	3,202
Income from continuing operations	3,883	4,047	8,001	7,555
Income (loss) from discontinued operations, net of taxes	21	(23)	3	(25)
Net income before attribution of noncontrolling interests	3,904	4,024	8,004	7,530
Noncontrolling interests	32	26	42	31
Citigroup’s net income	3,872	3,998	7,962	7,499
Comprehensive income
Add: Other comprehensive income (loss)	514	511	1,978	3,244
Citigroup’s total comprehensive income	4,386	4,509	9,940	10,743
Add: Other comprehensive income attributable to noncontrolling interests	39	(50)	70	(23)
Add: Net income attributable to noncontrolling interests	32	26	42	31
Total comprehensive income	4,457	4,485	10,052	10,751
Reportable legal entities | Citigroup parent company
Revenues
Dividends from subsidiaries	2,515	2,900	6,265	5,700
Interest revenue	(1)	1	0	3
Interest revenue—intercompany	1,076	668	1,869	1,540
Interest expense	1,136	1,094	2,354	2,164
Interest expense—intercompany	263	38	353	79
Net interest revenue	(324)	(463)	(838)	(700)
Commissions and fees	0	0	0	0
Commissions and fees—intercompany	(1)	(17)	(1)	(19)
Principal transactions	1,122	(186)	959	(395)
Principal transactions—intercompany	396	(217)	600	41
Other income	(1,601)	(585)	(1,640)	(3,679)
Other income—intercompany	161	736	38	3,996
Total non-interest revenues	77	(269)	(44)	(56)
Total revenues, net of interest expense	2,268	2,168	5,383	4,944
Provisions for credit losses and for benefits and claims	0	0	0	0
Operating expenses
Compensation and benefits	(1)	(16)	(15)	(8)
Compensation and benefits—intercompany	20	23	51	26
Other operating	(344)	213	(316)	480
Other operating—intercompany	10	79	(49)	80
Total operating expenses	(315)	299	(329)	578
Equity in undistributed income of subsidiaries	1,183	1,709	1,770	2,653
Income (loss) from continuing operations before income taxes	3,766	3,578	7,482	7,019
Provision for income taxes	(106)	(420)	(480)	(480)
Income from continuing operations	3,872	3,998	7,962	7,499
Income (loss) from discontinued operations, net of taxes	0	0	0	0
Net income before attribution of noncontrolling interests	3,872	3,998	7,962	7,499
Noncontrolling interests	0	0	0	0
Citigroup’s net income	3,872	3,998	7,962	7,499
Comprehensive income
Add: Other comprehensive income (loss)	514	511	1,978	3,244
Citigroup’s total comprehensive income	4,386	4,509	9,940	10,743
Add: Other comprehensive income attributable to noncontrolling interests	0	0	0	0
Add: Net income attributable to noncontrolling interests	0	0	0	0
Total comprehensive income	4,386	4,509	9,940	10,743
Reportable legal entities | CGMHI
Revenues
Dividends from subsidiaries	0	0	0	0
Interest revenue	1,404	1,251	2,431	2,397
Interest revenue—intercompany	377	139	534	275
Interest expense	546	401	942	765
Interest expense—intercompany	653	416	1,079	845
Net interest revenue	582	573	944	1,062
Commissions and fees	1,279	1,119	2,534	2,079
Commissions and fees—intercompany	108	(24)	110	(30)
Principal transactions	398	2,394	2,004	2,257
Principal transactions—intercompany	290	(1,791)	(392)	(1,043)
Other income	87	51	161	127
Other income—intercompany	(7)	339	27	199
Total non-interest revenues	2,155	2,088	4,444	3,589
Total revenues, net of interest expense	2,737	2,661	5,388	4,651
Provisions for credit losses and for benefits and claims	1	0	1	0
Operating expenses
Compensation and benefits	1,212	1,202	2,474	2,491
Compensation and benefits—intercompany	0	0	0	0
Other operating	443	412	849	798
Other operating—intercompany	502	322	970	629
Total operating expenses	2,157	1,936	4,293	3,918
Equity in undistributed income of subsidiaries	0	0	0	0
Income (loss) from continuing operations before income taxes	579	725	1,094	733
Provision for income taxes	261	157	476	194
Income from continuing operations	318	568	618	539
Income (loss) from discontinued operations, net of taxes	0	0	0	0
Net income before attribution of noncontrolling interests	318	568	618	539
Noncontrolling interests	0	(3)	0	(1)
Citigroup’s net income	318	571	618	540
Comprehensive income
Add: Other comprehensive income (loss)	(38)	58	(58)	105
Citigroup’s total comprehensive income	280	629	560	645
Add: Other comprehensive income attributable to noncontrolling interests	0	0	0	0
Add: Net income attributable to noncontrolling interests	0	(3)	0	(1)
Total comprehensive income	280	626	560	644
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Revenues
Dividends from subsidiaries	0	0	0	0
Interest revenue	13,798	13,104	27,193	26,123
Interest revenue—intercompany	(1,453)	(807)	(2,403)	(1,815)
Interest expense	2,354	1,625	4,306	3,131
Interest expense—intercompany	(916)	(454)	(1,432)	(924)
Net interest revenue	10,907	11,126	21,916	22,101
Commissions and fees	1,658	1,606	3,162	3,109
Commissions and fees—intercompany	(107)	41	(109)	49
Principal transactions	1,042	(392)	2,621	1,794
Principal transactions—intercompany	(686)	2,008	(208)	1,002
Other income	2,751	2,305	4,198	7,348
Other income—intercompany	(154)	(1,075)	(65)	(4,195)
Total non-interest revenues	4,504	4,493	9,599	9,107
Total revenues, net of interest expense	15,411	15,619	31,515	31,208
Provisions for credit losses and for benefits and claims	1,716	1,409	3,378	3,454
Operating expenses
Compensation and benefits	4,252	4,043	8,538	8,302
Compensation and benefits—intercompany	(20)	(23)	(51)	(26)
Other operating	4,944	4,515	9,453	8,829
Other operating—intercompany	(512)	(401)	(921)	(709)
Total operating expenses	8,664	8,134	17,019	16,396
Equity in undistributed income of subsidiaries	0	0	0	0
Income (loss) from continuing operations before income taxes	5,031	6,076	11,118	11,358
Provision for income taxes	1,640	1,986	3,662	3,488
Income from continuing operations	3,391	4,090	7,456	7,870
Income (loss) from discontinued operations, net of taxes	21	(23)	3	(25)
Net income before attribution of noncontrolling interests	3,412	4,067	7,459	7,845
Noncontrolling interests	32	29	42	32
Citigroup’s net income	3,380	4,038	7,417	7,813
Comprehensive income
Add: Other comprehensive income (loss)	(155)	1,708	(3,876)	1,173
Citigroup’s total comprehensive income	3,225	5,746	3,541	8,986
Add: Other comprehensive income attributable to noncontrolling interests	39	(50)	70	(23)
Add: Net income attributable to noncontrolling interests	32	29	42	32
Total comprehensive income	3,296	5,725	3,653	8,995
Consolidating adjustments
Revenues
Dividends from subsidiaries	(2,515)	(2,900)	(6,265)	(5,700)
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	(2,515)	(2,900)	(6,265)	(5,700)
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	(1,183)	(1,709)	(1,770)	(2,653)
Income (loss) from continuing operations before income taxes	(3,698)	(4,609)	(8,035)	(8,353)
Provision for income taxes	0	0	0	0
Income from continuing operations	(3,698)	(4,609)	(8,035)	(8,353)
Income (loss) from discontinued operations, net of taxes	0	0	0	0
Net income before attribution of noncontrolling interests	(3,698)	(4,609)	(8,035)	(8,353)
Noncontrolling interests	0	0	0	0
Citigroup’s net income	(3,698)	(4,609)	(8,035)	(8,353)
Comprehensive income
Add: Other comprehensive income (loss)	193	(1,766)	3,934	(1,278)
Citigroup’s total comprehensive income	(3,505)	(6,375)	(4,101)	(9,631)
Add: Other comprehensive income attributable to noncontrolling interests	0	0	0	0
Add: Net income attributable to noncontrolling interests	0	0	0	0
Total comprehensive income	$ (3,505)	$ (6,375)	$ (4,101)	$ (9,631)