CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Millions		Total	Citigroup stockholders' equity	Preferred stock at aggregate liquidation value	Citigroup common stockholders' equity	Common stock and additional paid-in capital	Retained earnings		Treasury stock, at cost		Citigroup's accumulated other comprehensive income (loss)		Noncontrolling interests
Increase (Decrease) in Stockholders' Equity
Adjusted balance							$ 145,817				$ (31,877)
Balance, beginning of year at Dec. 31, 2016				$ 19,253		$ 108,073	146,477		$ (16,302)		(32,381)		$ 1,023
Balance, beginning of year (in shares) at Dec. 31, 2016				770		3,099,482			327,090
Adjustment to opening balance, net of taxes at Dec. 31, 2016	[1]						(660)				504
Increase (Decrease) in Stockholders' Equity
Citigroup’s net income (loss)		$ (6,798)					(6,798)
Employee benefit plans						$ (27)			$ 531	[2]
Employee benefit plans (in shares)						41			11,651	[2]
Other						$ (7)	(90)	[3]					(72)
Net income attributable to noncontrolling-interest shareholders		(6,738)											60
Common dividends	[4]						(2,595)
Preferred dividends		(1,213)					(1,213)
Impact of Tax Reform							3,304	[5]			(3,304)
Transactions between noncontrolling-interest shareholders and the related consolidated subsidiary													(28)
Transactions between Citigroup and the noncontrolling-interest shareholders													(121)
Treasury stock acquired	[6]								$ (14,538)
Treasure stock acquired (in shares)	[6]								(214,176)
Distributions paid to noncontrolling-interest shareholders													(44)
Other comprehensive income (loss)		(2,791)									(2,791)	[5]	114
Net change in noncontrolling interests													(91)
Balance, end of year at Dec. 31, 2017		201,672	$ 200,740	$ 19,253	$ 181,487	$ 108,039	138,425		$ (30,309)		(34,668)		932
Balance, end of year (in shares) at Dec. 31, 2017				770	2,569,908	3,099,523			529,615
Increase (Decrease) in Stockholders' Equity
Adjusted balance							138,341				(34,671)
Adjustment to opening balance, net of taxes at Dec. 31, 2017	[1]						(84)				(3)
Increase (Decrease) in Stockholders' Equity
Citigroup’s net income (loss)		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]
Other						$ 8							18
Net income attributable to noncontrolling-interest shareholders		18,080											35
Common dividends	[4]						(3,865)
Preferred dividends		(1,174)					(1,174)
Transactions between Citigroup and the noncontrolling-interest shareholders													(50)
Treasury stock acquired	[6]								$ (14,545)
Treasure stock acquired (in shares)	[6]								(212,042)
Distributions paid to noncontrolling-interest shareholders													(38)
Other comprehensive income (loss)		(2,499)									(2,499)	[5]	(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		$ (44,370)		(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
Adjusted balance							151,498				(37,170)
Adjustment to opening balance, net of taxes at Dec. 31, 2018	[1]						151				0
Increase (Decrease) in Stockholders' Equity
Citigroup’s net income (loss)		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)
Other						34	(18)	[3]					(7)
Net income attributable to noncontrolling-interest shareholders		19,467											66
Common dividends	[4]						(4,403)
Preferred dividends		(1,109)					(1,109)
Transactions between Citigroup and the noncontrolling-interest shareholders													(169)
Treasury stock acquired	[6]								$ (17,875)
Treasure stock acquired (in shares)	[6]								(264,252)
Distributions paid to noncontrolling-interest shareholders													(40)
Other comprehensive income (loss)		852									852	[5]	0
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		$ (61,660)		$ (36,318)		$ 704
Balance, end of year (in shares) at Dec. 31, 2019				719	2,114,123	3,099,603			985,480

[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] 2017 includes the impact of ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. See Note 1 to the Consolidated Financial Statements.

[4] Common dividends declared were $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; $0.32 per share in the first and second quarters of 2018 and $0.45 per share in the third and fourth quarters of 2018; and $0.16 in the first and second quarters of 2017 and $0.32 per share in the third and fourth quarters of 2017.

[5] Includes the impact of ASU 2018-02, which transferred those amounts from AOCI to 2017 Retained earnings. See Notes 1 and 19 to the Consolidated Financial Statements.

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