CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets
Cash	$ 22,272	$ 23,043	$ 22,240	$ 20,900
Cash and due from banks—intercompany	0	0
Federal funds sold and securities borrowed or purchased under agreements to resell (including $137,360 and $133,204 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	242,929	236,813
Federal funds sold and resale agreements—intercompany	0	0
Trading account assets	244,903	243,925
Trading account assets—intercompany	0	0
Investments	345,833	353,304
Loans, net of unearned income	628,595	624,369
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	(12,030)	(12,060)	(12,712)	$ (12,626)
Total loans, net	616,565	612,309
Advances to subsidiaries	0	0
Investments in subsidiaries	0	0
Other assets	349,133	322,683
Other assets—intercompany	0	0
Total assets	1,821,635	1,792,077
Liabilities and equity
Deposits	949,990	929,406
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $40,939 and $33,663 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	148,230	141,821
Federal funds purchased and securities loaned or sold—intercompany	0	0
Trading account liabilities	144,070	139,045
Trading account liabilities—intercompany	0	0
Short-term borrowings, at fair value	26,127	30,701
Short-term borrowings—intercompany	0	0
Long-term debt	208,530	206,178
Long-term debt—intercompany	0	0
Advances from subsidiaries	0	0
Other liabilities	115,535	118,783
Other liabilities—intercompany	0	0
Stockholders’ equity	229,153	226,143	$ 228,761
Total liabilities and equity	1,821,635	1,792,077
Other	126,627	128,008
Citigroup parent company
Liabilities and equity
Long-term debt	141,626	147,333
Citibank, N.A.
Liabilities and equity
Other	18,200	20,700
Reportable legal entities | Citigroup parent company
Assets
Cash	0	0
Cash and due from banks—intercompany	352	142
Federal funds sold and securities borrowed or purchased under agreements to resell (including $137,360 and $133,204 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	0	0
Federal funds sold and resale agreements—intercompany	0	0
Trading account assets	1	6
Trading account assets—intercompany	991	1,173
Investments	43	173
Loans, net of unearned income	0	0
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	0	0
Total loans, net	0	0
Advances to subsidiaries	143,808	143,154
Investments in subsidiaries	228,432	226,279
Other assets	23,924	23,734
Other assets—intercompany	8,229	27,845
Total assets	405,780	422,506
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $40,939 and $33,663 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	0	0
Federal funds purchased and securities loaned or sold—intercompany	0	0
Trading account liabilities	7	0
Trading account liabilities—intercompany	819	1,006
Short-term borrowings, at fair value	0	0
Short-term borrowings—intercompany	0	0
Long-term debt	141,626	147,333
Long-term debt—intercompany	0	0
Advances from subsidiaries	26,357	41,258
Other liabilities	3,346	3,466
Other liabilities—intercompany	5,493	4,323
Stockholders’ equity	228,132	225,120
Total liabilities and equity	405,780	422,506
Reportable legal entities | CGMHI
Assets
Cash	480	870
Cash and due from banks—intercompany	3,167	3,820
Federal funds sold and securities borrowed or purchased under agreements to resell (including $137,360 and $133,204 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	196,387	196,236
Federal funds sold and resale agreements—intercompany	14,742	12,270
Trading account assets	128,414	121,484
Trading account assets—intercompany	3,173	907
Investments	217	335
Loans, net of unearned income	1,269	575
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	0	0
Total loans, net	1,269	575
Advances to subsidiaries	0	0
Investments in subsidiaries	0	0
Other assets	51,968	46,095
Other assets—intercompany	58,770	38,207
Total assets	458,587	420,799
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $40,939 and $33,663 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	128,196	122,320
Federal funds purchased and securities loaned or sold—intercompany	20,807	25,417
Trading account liabilities	94,791	87,714
Trading account liabilities—intercompany	2,834	868
Short-term borrowings, at fair value	1,961	1,356
Short-term borrowings—intercompany	65,562	35,596
Long-term debt	15,017	8,128
Long-term debt—intercompany	28,781	41,287
Advances from subsidiaries	0	0
Other liabilities	66,324	57,430
Other liabilities—intercompany	1,263	7,894
Stockholders’ equity	33,051	32,789
Total liabilities and equity	458,587	420,799
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Assets
Cash	21,792	22,173
Cash and due from banks—intercompany	(3,519)	(3,962)
Federal funds sold and securities borrowed or purchased under agreements to resell (including $137,360 and $133,204 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	46,542	40,577
Federal funds sold and resale agreements—intercompany	(14,742)	(12,270)
Trading account assets	116,488	122,435
Trading account assets—intercompany	(4,164)	(2,080)
Investments	345,573	352,796
Loans, net of unearned income	627,326	623,794
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	(12,030)	(12,060)
Total loans, net	615,296	611,734
Advances to subsidiaries	(143,808)	(143,154)
Investments in subsidiaries	0	0
Other assets	273,241	252,854
Other assets—intercompany	(66,999)	(66,052)
Total assets	1,185,700	1,175,051
Liabilities and equity
Deposits	949,990	929,406
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $40,939 and $33,663 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	20,034	19,501
Federal funds purchased and securities loaned or sold—intercompany	(20,807)	(25,417)
Trading account liabilities	49,272	51,331
Trading account liabilities—intercompany	(3,653)	(1,874)
Short-term borrowings, at fair value	24,166	29,345
Short-term borrowings—intercompany	(65,562)	(35,596)
Long-term debt	51,887	50,717
Long-term debt—intercompany	(28,781)	(41,287)
Advances from subsidiaries	(26,357)	(41,258)
Other liabilities	45,865	57,887
Other liabilities—intercompany	(6,756)	(12,217)
Stockholders’ equity	196,402	194,513
Total liabilities and equity	1,185,700	1,175,051
Consolidating adjustments
Assets
Cash	0	0
Cash and due from banks—intercompany	0	0
Federal funds sold and securities borrowed or purchased under agreements to resell (including $137,360 and $133,204 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	0	0
Federal funds sold and resale agreements—intercompany	0	0
Trading account assets	0	0
Trading account assets—intercompany	0	0
Investments	0	0
Loans, net of unearned income	0	0
Loans, net of unearned income—intercompany	0	0
Allowance for loan losses	0	0
Total loans, net	0	0
Advances to subsidiaries	0	0
Investments in subsidiaries	(228,432)	(226,279)
Other assets	0	0
Other assets—intercompany	0	0
Total assets	(228,432)	(226,279)
Liabilities and equity
Deposits	0	0
Deposits—intercompany	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $40,939 and $33,663 as of March 31, 2017 and December 31, 2016, respectively, at fair value)	0	0
Federal funds purchased and securities loaned or sold—intercompany	0	0
Trading account liabilities	0	0
Trading account liabilities—intercompany	0	0
Short-term borrowings, at fair value	0	0
Short-term borrowings—intercompany	0	0
Long-term debt	0	0
Long-term debt—intercompany	0	0
Advances from subsidiaries	0	0
Other liabilities	0	0
Other liabilities—intercompany	0	0
Stockholders’ equity	(228,432)	(226,279)
Total liabilities and equity	(228,432)	(226,279)
Up to 30 days | Citibank, N.A.
Liabilities and equity
Placements with term of less than 30 days	$ 8,300	$ 6,800