CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues
Dividends from subsidiaries	$ 0	$ 0
Interest revenue	17,139	19,076
Interest revenue—intercompany	0	0
Interest expense	5,647	7,317
Interest expense—intercompany	0	0
Net interest revenue	11,492	11,759
Commissions and fees	3,021	2,926
Commissions and fees—intercompany	0	0
Principal transactions	5,261	2,804
Principal transactions—intercompany	0	0
Other income	957	1,087
Other income—intercompany	0	0
Total non-interest revenues	9,239	6,817
Total revenues, net of interest expense	20,731	18,576
Total provisions for credit losses and for benefits and claims	7,027	1,980
Operating expenses
Compensation and benefits	5,654	5,658
Compensation and benefits—intercompany	0	0
Other operating	4,940	4,926
Other operating—intercompany	0	0
Total operating expenses	10,594	10,584
Equity in undistributed income of subsidiaries	0	0
Income (loss) from continuing operations before income taxes	3,110	6,012
Provision for income taxes	576	1,275
Income from continuing operations	2,534	4,737
Loss from discontinued operations, net of taxes	(18)	(2)
Net income before attribution of noncontrolling interests	2,516	4,735
Noncontrolling interests	(6)	25
Citigroup’s net income	2,522	4,710
Comprehensive income
Add: Other comprehensive income (loss)	3,797	862
Citigroup’s total comprehensive income	6,319	5,572
Add: Other comprehensive income (loss) attributable to noncontrolling interests	(51)	(13)
Add: Net income attributable to noncontrolling interests	(6)	25
Total comprehensive income (loss)	6,262	5,584
Reportable legal entities | Citigroup parent company
Revenues
Dividends from subsidiaries	105	9,167
Interest revenue	0	0
Interest revenue—intercompany	1,144	1,325
Interest expense	1,143	1,271
Interest expense—intercompany	248	312
Net interest revenue	(247)	(258)
Commissions and fees	0	0
Commissions and fees—intercompany	(19)	(1)
Principal transactions	(672)	(825)
Principal transactions—intercompany	502	447
Other income	80	319
Other income—intercompany	(70)	(34)
Total non-interest revenues	(179)	(94)
Total revenues, net of interest expense	(321)	8,815
Total provisions for credit losses and for benefits and claims	0	0
Operating expenses
Compensation and benefits	28	33
Compensation and benefits—intercompany	74	26
Other operating	23	5
Other operating—intercompany	4	5
Total operating expenses	129	69
Equity in undistributed income of subsidiaries	2,368	(4,203)
Income (loss) from continuing operations before income taxes	1,918	4,543
Provision for income taxes	(604)	(167)
Income from continuing operations	2,522	4,710
Loss from discontinued operations, net of taxes	0	0
Net income before attribution of noncontrolling interests	2,522	4,710
Noncontrolling interests	0	0
Citigroup’s net income	2,522	4,710
Comprehensive income
Add: Other comprehensive income (loss)	3,797	862
Citigroup’s total comprehensive income	6,319	5,572
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0
Add: Net income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	6,319	5,572
Reportable legal entities | CGMHI
Revenues
Dividends from subsidiaries	0	0
Interest revenue	1,903	2,572
Interest revenue—intercompany	341	503
Interest expense	1,141	1,824
Interest expense—intercompany	782	1,075
Net interest revenue	321	176
Commissions and fees	1,550	1,307
Commissions and fees—intercompany	164	121
Principal transactions	6,254	(1,034)
Principal transactions—intercompany	(4,391)	2,036
Other income	49	99
Other income—intercompany	13	42
Total non-interest revenues	3,639	2,571
Total revenues, net of interest expense	3,960	2,747
Total provisions for credit losses and for benefits and claims	(1)	0
Operating expenses
Compensation and benefits	1,296	1,284
Compensation and benefits—intercompany	0	0
Other operating	598	553
Other operating—intercompany	482	582
Total operating expenses	2,376	2,419
Equity in undistributed income of subsidiaries	0	0
Income (loss) from continuing operations before income taxes	1,585	328
Provision for income taxes	337	140
Income from continuing operations	1,248	188
Loss from discontinued operations, net of taxes	0	0
Net income before attribution of noncontrolling interests	1,248	188
Noncontrolling interests	0	0
Citigroup’s net income	1,248	188
Comprehensive income
Add: Other comprehensive income (loss)	1,757	(289)
Citigroup’s total comprehensive income	3,005	(101)
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0
Add: Net income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	3,005	(101)
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Revenues
Dividends from subsidiaries	0	0
Interest revenue	15,236	16,504
Interest revenue—intercompany	(1,485)	(1,828)
Interest expense	3,363	4,222
Interest expense—intercompany	(1,030)	(1,387)
Net interest revenue	11,418	11,841
Commissions and fees	1,471	1,619
Commissions and fees—intercompany	(145)	(120)
Principal transactions	(321)	4,663
Principal transactions—intercompany	3,889	(2,483)
Other income	828	669
Other income—intercompany	57	(8)
Total non-interest revenues	5,779	4,340
Total revenues, net of interest expense	17,197	16,181
Total provisions for credit losses and for benefits and claims	7,028	1,980
Operating expenses
Compensation and benefits	4,330	4,341
Compensation and benefits—intercompany	(74)	(26)
Other operating	4,319	4,368
Other operating—intercompany	(486)	(587)
Total operating expenses	8,089	8,096
Equity in undistributed income of subsidiaries	0	0
Income (loss) from continuing operations before income taxes	2,080	6,105
Provision for income taxes	843	1,302
Income from continuing operations	1,237	4,803
Loss from discontinued operations, net of taxes	(18)	(2)
Net income before attribution of noncontrolling interests	1,219	4,801
Noncontrolling interests	(6)	25
Citigroup’s net income	1,225	4,776
Comprehensive income
Add: Other comprehensive income (loss)	1,179	999
Citigroup’s total comprehensive income	2,404	5,775
Add: Other comprehensive income (loss) attributable to noncontrolling interests	(51)	(13)
Add: Net income attributable to noncontrolling interests	(6)	25
Total comprehensive income (loss)	2,347	5,787
Consolidating adjustments
Revenues
Dividends from subsidiaries	(105)	(9,167)
Interest revenue	0	0
Interest revenue—intercompany	0	0
Interest expense	0	0
Interest expense—intercompany	0	0
Net interest revenue	0	0
Commissions and fees	0	0
Commissions and fees—intercompany	0	0
Principal transactions	0	0
Principal transactions—intercompany	0	0
Other income	0	0
Other income—intercompany	0	0
Total non-interest revenues	0	0
Total revenues, net of interest expense	(105)	(9,167)
Total provisions for credit losses and for benefits and claims	0	0
Operating expenses
Compensation and benefits	0	0
Compensation and benefits—intercompany	0	0
Other operating	0	0
Other operating—intercompany	0	0
Total operating expenses	0	0
Equity in undistributed income of subsidiaries	(2,368)	4,203
Income (loss) from continuing operations before income taxes	(2,473)	(4,964)
Provision for income taxes	0	0
Income from continuing operations	(2,473)	(4,964)
Loss from discontinued operations, net of taxes	0	0
Net income before attribution of noncontrolling interests	(2,473)	(4,964)
Noncontrolling interests	0	0
Citigroup’s net income	(2,473)	(4,964)
Comprehensive income
Add: Other comprehensive income (loss)	(2,936)	(710)
Citigroup’s total comprehensive income	(5,409)	(5,674)
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0
Add: Net income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	$ (5,409)	$ (5,674)