CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Statements of Income and Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues
Dividends from subsidiaries	$ 0	$ 0
Interest revenue	19,076	16,332
Interest revenue—intercompany	0	0
Interest expense	7,317	5,160
Interest expense—intercompany	0	0
Net interest revenue	11,759	11,172
Commissions and fees	2,926	3,030
Commissions and fees—intercompany	0	0
Principal transactions	2,804	3,242
Principal transactions—intercompany	0	0
Other income	1,087	1,428
Other income—intercompany	0	0
Total non-interest revenues	6,817	7,700
Total revenues, net of interest expense	18,576	18,872
Provisions for credit losses and for benefits and claims	1,980	1,857
Operating expenses
Compensation and benefits	5,658	5,807
Compensation and benefits—intercompany	0	0
Other operating	4,926	5,118
Other operating—intercompany	0	0
Total operating expenses	10,584	10,925
Equity in undistributed income of subsidiaries	0	0
Income (loss) from continuing operations before income taxes	6,012	6,090
Provision for income taxes	1,275	1,441
Income from continuing operations	4,737	4,649
Loss from discontinued operations, net of taxes	(2)	(7)
Net income before attribution of noncontrolling interests	4,735	4,642
Noncontrolling interests	25	22
Citigroup’s net income	4,710	4,620
Comprehensive income
Add: Other comprehensive income (loss)	862	52
Citigroup’s total comprehensive income	5,572	4,672
Add: Other comprehensive income (loss) attributable to noncontrolling interests	(13)	14
Add: Net income attributable to noncontrolling interests	25	22
Total comprehensive income (loss)	5,584	4,708
Reportable legal entities | Citigroup parent company
Revenues
Dividends from subsidiaries	9,167	5,585
Interest revenue	0	52
Interest revenue—intercompany	1,325	1,130
Interest expense	1,271	1,238
Interest expense—intercompany	312	259
Net interest revenue	(258)	(315)
Commissions and fees	0	0
Commissions and fees—intercompany	(1)	0
Principal transactions	(825)	1,031
Principal transactions—intercompany	447	(386)
Other income	319	(928)
Other income—intercompany	(34)	55
Total non-interest revenues	(94)	(228)
Total revenues, net of interest expense	8,815	5,042
Provisions for credit losses and for benefits and claims	0	0
Operating expenses
Compensation and benefits	33	134
Compensation and benefits—intercompany	26	34
Other operating	5	43
Other operating—intercompany	5	12
Total operating expenses	69	223
Equity in undistributed income of subsidiaries	(4,203)	(446)
Income (loss) from continuing operations before income taxes	4,543	4,373
Provision for income taxes	(167)	(247)
Income from continuing operations	4,710	4,620
Loss from discontinued operations, net of taxes	0	0
Net income before attribution of noncontrolling interests	4,710	4,620
Noncontrolling interests	0	0
Citigroup’s net income	4,710	4,620
Comprehensive income
Add: Other comprehensive income (loss)	862	52
Citigroup’s total comprehensive income	5,572	4,672
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0
Add: Net income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	5,572	4,672
Reportable legal entities | CGMHI
Revenues
Dividends from subsidiaries	0	0
Interest revenue	2,572	1,656
Interest revenue—intercompany	503	383
Interest expense	1,824	1,013
Interest expense—intercompany	1,075	772
Net interest revenue	176	254
Commissions and fees	1,307	1,252
Commissions and fees—intercompany	121	0
Principal transactions	(1,034)	921
Principal transactions—intercompany	2,036	192
Other income	99	153
Other income—intercompany	42	55
Total non-interest revenues	2,571	2,573
Total revenues, net of interest expense	2,747	2,827
Provisions for credit losses and for benefits and claims	0	0
Operating expenses
Compensation and benefits	1,284	1,265
Compensation and benefits—intercompany	0	0
Other operating	553	550
Other operating—intercompany	582	582
Total operating expenses	2,419	2,397
Equity in undistributed income of subsidiaries	0	0
Income (loss) from continuing operations before income taxes	328	430
Provision for income taxes	140	65
Income from continuing operations	188	365
Loss from discontinued operations, net of taxes	0	0
Net income before attribution of noncontrolling interests	188	365
Noncontrolling interests	0	0
Citigroup’s net income	188	365
Comprehensive income
Add: Other comprehensive income (loss)	(289)	82
Citigroup’s total comprehensive income	(101)	447
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0
Add: Net income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	(101)	447
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Revenues
Dividends from subsidiaries	0	0
Interest revenue	16,504	14,624
Interest revenue—intercompany	(1,828)	(1,513)
Interest expense	4,222	2,909
Interest expense—intercompany	(1,387)	(1,031)
Net interest revenue	11,841	11,233
Commissions and fees	1,619	1,778
Commissions and fees—intercompany	(120)	0
Principal transactions	4,663	1,290
Principal transactions—intercompany	(2,483)	194
Other income	669	2,203
Other income—intercompany	(8)	(110)
Total non-interest revenues	4,340	5,355
Total revenues, net of interest expense	16,181	16,588
Provisions for credit losses and for benefits and claims	1,980	1,857
Operating expenses
Compensation and benefits	4,341	4,408
Compensation and benefits—intercompany	(26)	(34)
Other operating	4,368	4,525
Other operating—intercompany	(587)	(594)
Total operating expenses	8,096	8,305
Equity in undistributed income of subsidiaries	0	0
Income (loss) from continuing operations before income taxes	6,105	6,426
Provision for income taxes	1,302	1,623
Income from continuing operations	4,803	4,803
Loss from discontinued operations, net of taxes	(2)	(7)
Net income before attribution of noncontrolling interests	4,801	4,796
Noncontrolling interests	25	22
Citigroup’s net income	4,776	4,774
Comprehensive income
Add: Other comprehensive income (loss)	999	(3,156)
Citigroup’s total comprehensive income	5,775	1,618
Add: Other comprehensive income (loss) attributable to noncontrolling interests	(13)	14
Add: Net income attributable to noncontrolling interests	25	22
Total comprehensive income (loss)	5,787	1,654
Consolidating adjustments
Revenues
Dividends from subsidiaries	(9,167)	(5,585)
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	(9,167)	(5,585)
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	4,203	446
Income (loss) from continuing operations before income taxes	(4,964)	(5,139)
Provision for income taxes	0	0
Income from continuing operations	(4,964)	(5,139)
Loss from discontinued operations, net of taxes	0	0
Net income before attribution of noncontrolling interests	(4,964)	(5,139)
Noncontrolling interests	0	0
Citigroup’s net income	(4,964)	(5,139)
Comprehensive income
Add: Other comprehensive income (loss)	(710)	3,074
Citigroup’s total comprehensive income	(5,674)	(2,065)
Add: Other comprehensive income (loss) attributable to noncontrolling interests	0	0
Add: Net income attributable to noncontrolling interests	0	0
Total comprehensive income (loss)	$ (5,674)	$ (2,065)