CONDENSED CONSOLIDATING FINANCIAL STATEMENTS - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Assets
Cash	$ 23,419		$ 20,900	$ 21,726		$ 32,108
Cash and due from banks—intercompany	0		0
Federal funds sold and securities borrowed or purchased under agreements to resell (including $143,618 and $137,964 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	236,045		219,675
Federal funds sold and resale agreements—intercompany	0		0
Trading account assets	263,352		249,956
Trading account assets—intercompany	0		0
Investments	354,940		342,955
Loans, net of unearned income	638,435		617,617
Loans, net of unearned income—intercompany	0		0
Allowance for loan losses	(12,439)	$ (12,304)	(12,626)	(13,626)	$ (14,075)	$ (15,994)
Total loans, net	625,996		604,991
Advances to subsidiaries	0		0
Investments in subsidiaries	0		0
Other assets	314,365		292,733
Other assets—intercompany	0		0
Total assets	1,818,117		1,731,210
Liabilities and equity
Deposits	940,252		907,887
Deposits—intercompany	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $42,939 and $36,843 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	153,124		146,496
Federal funds purchased and securities loaned or sold—intercompany	0		0
Trading account liabilities	131,649		117,512
Trading account liabilities—intercompany	0		0
Short-term borrowings, at fair value	29,527		21,079
Short-term borrowings—intercompany	0		0
Long-term debt, at fair value	209,051		201,275
Long-term debt—intercompany	0		0
Advances from subsidiaries	0		0
Other liabilities	121,824		113,869
Other liabilities—intercompany	0		0
Stockholders’ equity	232,690		223,092	$ 222,137
Total liabilities and equity	1,818,117		1,731,210
Other	116,515		125,002
Citigroup parent company
Liabilities and equity
Long-term debt, at fair value	149,042		142,157
Citibank, N.A.
Liabilities and equity
Other	18,200		21,800
Reportable legal entities | Citigroup parent company
Assets
Cash	0		0
Cash and due from banks—intercompany	131		124
Federal funds sold and securities borrowed or purchased under agreements to resell (including $143,618 and $137,964 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	0		0
Federal funds sold and resale agreements—intercompany	0		0
Trading account assets	(97)		(8)
Trading account assets—intercompany	656		1,032
Investments	193		484
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	115,107		104,405
Investments in subsidiaries	232,108		221,362
Other assets	24,243		25,819
Other assets—intercompany	55,500		58,207
Total assets	427,841		411,425
Liabilities and equity
Deposits	0		0
Deposits—intercompany	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $42,939 and $36,843 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	0		0
Federal funds purchased and securities loaned or sold—intercompany	0		185
Trading account liabilities	0		0
Trading account liabilities—intercompany	563		1,036
Short-term borrowings, at fair value	1		146
Short-term borrowings—intercompany	0		0
Long-term debt, at fair value	149,042		141,914
Long-term debt—intercompany	0		0
Advances from subsidiaries	34,135		36,453
Other liabilities	3,547		3,560
Other liabilities—intercompany	8,978		6,274
Stockholders’ equity	231,575		221,857
Total liabilities and equity	427,841		411,425
Reportable legal entities | CGMHI
Assets
Cash	593		592
Cash and due from banks—intercompany	2,241		1,403
Federal funds sold and securities borrowed or purchased under agreements to resell (including $143,618 and $137,964 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	197,446		178,178
Federal funds sold and resale agreements—intercompany	8,164		15,035
Trading account assets	141,187		124,731
Trading account assets—intercompany	1,148		1,765
Investments	353		402
Loans, net of unearned income	749		1,068
Loans, net of unearned income—intercompany	0		0
Allowance for loan losses	0		(3)
Total loans, net	749		1,065
Advances to subsidiaries	0		0
Investments in subsidiaries	0		0
Other assets	40,433		36,860
Other assets—intercompany	32,526		30,737
Total assets	424,840		390,768
Liabilities and equity
Deposits	0		0
Deposits—intercompany	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $42,939 and $36,843 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	133,214		122,459
Federal funds purchased and securities loaned or sold—intercompany	23,538		22,042
Trading account liabilities	84,252		62,386
Trading account liabilities—intercompany	1,303		2,045
Short-term borrowings, at fair value	1,439		188
Short-term borrowings—intercompany	34,190		34,916
Long-term debt, at fair value	6,993		2,530
Long-term debt—intercompany	38,573		51,171
Advances from subsidiaries	0		0
Other liabilities	68,047		55,482
Other liabilities—intercompany	704		10,967
Stockholders’ equity	32,587		26,582
Total liabilities and equity	424,840		390,768
Reportable legal entities | Other Citigroup subsidiaries and eliminations
Assets
Cash	22,826		20,308
Cash and due from banks—intercompany	(2,372)		(1,527)
Federal funds sold and securities borrowed or purchased under agreements to resell (including $143,618 and $137,964 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	38,599		41,497
Federal funds sold and resale agreements—intercompany	(8,164)		(15,035)
Trading account assets	122,262		125,233
Trading account assets—intercompany	(1,804)		(2,797)
Investments	354,394		342,069
Loans, net of unearned income	637,686		616,549
Loans, net of unearned income—intercompany	0		0
Allowance for loan losses	(12,439)		(12,623)
Total loans, net	625,247		603,926
Advances to subsidiaries	(115,107)		(104,405)
Investments in subsidiaries	0		0
Other assets	249,689		230,054
Other assets—intercompany	(88,026)		(88,944)
Total assets	1,197,544		1,150,379
Liabilities and equity
Deposits	940,252		907,887
Deposits—intercompany	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $42,939 and $36,843 as of September 30, 2016 and December 31, 2015, respectively, at fair value)	19,910		24,037
Federal funds purchased and securities loaned or sold—intercompany	(23,538)		(22,227)
Trading account liabilities	47,397		55,126
Trading account liabilities—intercompany	(1,866)		(3,081)
Short-term borrowings, at fair value	28,087		20,745
Short-term borrowings—intercompany	(34,190)		(34,916)
Long-term debt, at fair value	53,016		56,831
Long-term debt—intercompany	(38,573)		(51,171)
Advances from subsidiaries	(34,135)		(36,453)
Other liabilities	50,230		54,827
Other liabilities—intercompany	(9,682)		(17,241)
Stockholders’ equity	200,636		196,015
Total liabilities and equity	1,197,544		1,150,379
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 $143,618 and $137,964 as of September 30, 2016 and December 31, 2015, 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	(232,108)		(221,362)
Other assets	0		0
Other assets—intercompany	0		0
Total assets	(232,108)		(221,362)
Liabilities and equity
Deposits	0		0
Deposits—intercompany	0		0
Federal funds purchased and securities loaned or sold under agreements to repurchase (including $42,939 and $36,843 as of September 30, 2016 and December 31, 2015, 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, at fair value	0		0
Long-term debt—intercompany	0		0
Advances from subsidiaries	0		0
Other liabilities	0		0
Other liabilities—intercompany	0		0
Stockholders’ equity	(232,108)		(221,362)
Total liabilities and equity	(232,108)		(221,362)
Up to 30 days | Citibank, N.A.
Liabilities and equity
Placements with term of less than 30 days	$ 8,300		$ 13,900