CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Millions		Total	Revision of Prior Period, Change in Accounting Principle, Adjustment	Citigroup stockholders' equity	Preferred stock at aggregate liquidation value	Citigroup common stockholders' equity	Common stock and additional paid-in capital	Retained earnings	Retained earnings Previously Reported	Retained earnings Revision of Prior Period, Change in Accounting Principle, Adjustment	[1]	Retained earnings Cumulative Effect, Period of Adoption, Adjustment	[1]	Retained earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury stock, at cost		Citigroup's accumulated other comprehensive income (loss)		Citigroup's accumulated other comprehensive income (loss) Cumulative Effect, Period of Adoption, Adjustment	[1]	Citigroup's accumulated other comprehensive income (loss) Cumulative Effect, Period of Adoption, Adjusted Balance	Noncontrolling interests
Balance, beginning of year at Dec. 31, 2017					$ 19,253		$ 108,039	$ 138,425				$ (84)		$ 138,341	$ (30,309)		$ (34,668)		$ (3)		$ (34,671)	$ 932
Balance, beginning of year (in shares) at Dec. 31, 2017					770		3,099,523								529,615
Increase (Decrease) in Stockholders' Equity
Citigroup’s net income		$ 18,045						18,045
Redemption of preferred stock					$ (793)
Redemption of preferred stock (in shares)					(32)
Employee benefit plans							$ (94)								$ 484	[2]
Employee benefit plans (in shares)							44								10,557	[2]
Common dividends	[3]							(3,865)
Preferred dividends		(1,174)						(1,174)
Treasury stock acquired	[4]														$ (14,545)
Treasure stock acquired (in shares)	[4]														(212,042)
Other							$ 8															18
Transactions between Citigroup and the noncontrolling-interest shareholders																						(50)
Net income attributable to noncontrolling-interest shareholders		18,080																				35
Distributions paid to noncontrolling-interest shareholders																						(38)
Other comprehensive income (loss)																	(2,499)	[2]				(43)
Net change in noncontrolling interests																						(78)
Balance, end of year at Dec. 31, 2018		$ 197,074		$ 196,220	$ 18,460	$ 177,760	$ 107,953	151,347				151		151,498	$ (44,370)		(37,170)				(37,170)	854
Balance, end of year (in shares) at Dec. 31, 2018					738	2,368,467	3,099,567								731,100
Increase (Decrease) in Stockholders' Equity
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Change in Accounting Principle, Type [Extensible List]		us-gaap:ChangeInAccountingPrincipleMember
Citigroup’s net income		$ 19,401						19,401
Issuance of new preferred stock					$ 1,500
Issuance of new preferred stock (in shares)					60
Redemption of preferred stock					$ (1,980)
Redemption of preferred stock (in shares)					(79)
Employee benefit plans							$ (112)								$ 585	[2]
Employee benefit plans (in shares)							36								9,872	[2]
Preferred stock issuance expense							$ (4)
Common dividends	[3]							(4,403)
Preferred dividends		(1,109)						(1,109)
Treasury stock acquired	[4]														$ (17,875)
Treasure stock acquired (in shares)	[4]														(264,252)
Other							34	(18)														(7)
Transactions between Citigroup and the noncontrolling-interest shareholders																						(169)
Net income attributable to noncontrolling-interest shareholders		19,467																				66
Distributions paid to noncontrolling-interest shareholders																						(40)
Other comprehensive income (loss)	[2]																852
Net change in noncontrolling interests																						(150)
Balance, end of year at Dec. 31, 2019		193,946		193,242	$ 17,980	$ 175,262	$ 107,871	165,369	$ 165,369	$ 330		$ (3,076)		$ 162,623	$ (61,660)		(36,318)				$ (36,318)	704
Balance, end of year (in shares) at Dec. 31, 2019					719	2,114,123	3,099,603								985,480
Increase (Decrease) in Stockholders' Equity
Citigroup’s net income		11,047	$ (330)					11,047
Issuance of new preferred stock					$ 3,000
Issuance of new preferred stock (in shares)					120
Redemption of preferred stock					$ (1,500)
Redemption of preferred stock (in shares)					(60)
Employee benefit plans							$ 5								$ 456	[2]
Employee benefit plans (in shares)							161								8,546	[2]
Preferred stock issuance expense							$ (4)
Common dividends	[3]							(4,299)
Preferred dividends		(1,095)						(1,095)
Treasury stock acquired	[4]														$ (2,925)
Treasure stock acquired (in shares)	[4]														(40,740)
Other							5	(4)														(6)
Transactions between Citigroup and the noncontrolling-interest shareholders																						(4)
Net income attributable to noncontrolling-interest shareholders		11,087																				40
Distributions paid to noncontrolling-interest shareholders																						(2)
Other comprehensive income (loss)																	4,260	[2]				26
Net change in noncontrolling interests																						54
Balance, end of year at Dec. 31, 2020		$ 200,200		$ 199,442	$ 19,480	$ 179,962	$ 107,877	$ 168,272							$ (64,129)		$ (32,058)					$ 758
Balance, end of year (in shares) at Dec. 31, 2020					779	2,082,090	3,099,764								1,017,674

[1] See Note 1 to the Consolidated Financial Statements for additional details.

[2] Includes treasury stock related to (i) certain activity on employee stock option program exercises where the employee delivers existing shares to cover the option exercise, or (ii) under Citi’s employee restricted or deferred stock programs where shares are withheld to satisfy tax requirements.

[3] Common dividends declared were $0.51 per share in the first, second, third and fourth quarters of 2020; $0.45 per share in the first and second quarters of 2019 and $0.51 per share in the third and fourth quarters of 2019; and $0.32 in the first and second quarters of 2018 and $0.45 per share in the third and fourth quarters of 2018.

[4] Primarily consists of open market purchases under Citi’s Board of Directors-approved common stock repurchase programs.