EARNINGS PER SHARE (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended				9 Months Ended
	Dec. 17, 2012	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
EARNINGS PER SHARE
Income from continuing operations before attribution of noncontrolling interests		$ 3,186		$ 485		$ 11,305		$ 6,509
Less: Noncontrolling interests from continuing operations		51		25		177		191
Net income from continuing operations (for EPS purposes)		3,135		460		11,128		6,318
Income from discontinued operations, net of taxes		92		8		89		27
Citigroup's net income		3,227		468		11,217		6,345
Less: Preferred dividends		110		4		123		17
Net income available to common shareholders		3,117		464		11,094		6,328
Less: Dividends and undistributed earnings allocated to employee restricted and deferred shares that contain nonforfeitable rights to dividends, applicable to basic EPS		61		11		217		138
Net income allocated to common shareholders for basic		3,056		453		10,877		6,190
Add: Interest expense, net of tax, and dividends on convertible securities and adjustment of undistributed earnings allocated to employee restricted and deferred shares with nonforfeitable rights to dividends, applicable to diluted EPS				2		2		10
Net income allocated to common shareholders for diluted EPS		$ 3,056		$ 455		$ 10,879		$ 6,200
Weighted-average common shares outstanding applicable to basic EPS		3,034,300,000	[1]	2,926,800,000	[1]	3,038,400,000	[1]	2,926,500,000	[1]
Effect of dilutive securities
T-DECs (in shares)				87,800,000				87,800,000
Options (in shares)		6,100,000				5,000,000
Other employee plans (in shares)		500,000		600,000		500,000		500,000
Convertible securities (in shares)				100,000		100,000		100,000
Adjusted weighted-average common shares outstanding applicable to diluted EPS		3,040,900,000	[1]	3,015,300,000	[1]	3,044,000,000	[1]	3,014,900,000	[1]
Basic earnings per share
Income from continuing operations (in dollars per share)		$ 0.98	[1]	$ 0.15	[1]	$ 3.55	[1]	$ 2.11	[1]
Discontinued operations (in dollars per share)		$ 0.03	[1]			$ 0.03	[1]	$ 0.01	[1]
Net income (in dollars per share)		$ 1.01	[1]	$ 0.15	[1]	$ 3.58	[1]	$ 2.12	[1]
Diluted earnings per share
Income from continuing operations (in dollars per share)		$ 0.98	[1]	$ 0.15	[1]	$ 3.55	[1]	$ 2.05	[1]
Discontinued operations (in dollars per share)		$ 0.03	[1]			$ 0.03	[1]	$ 0.01	[1]
Net income (in dollars per share)		$ 1.00	[1]	$ 0.15	[1]	$ 3.57	[1]	$ 2.06	[1]
Number of shares delivered for the final settlement of the prepaid stock purchase contract	96,337,772
Weighted-average options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings per common share (in shares)		1,500,000		35,600,000
Antidilutive securities exercise price (in dollars per share)		$ 214.30		$ 51.97		$ 214.30		$ 51.97
Warrants issued to U.S. Treasury as part of TARP and loss-sharing agreement | Warrant with the exercise price of $178.50
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings per common share (in shares)		21,000,000		21,000,000
Antidilutive securities exercise price (in dollars per share)		$ 178.50		$ 178.50		$ 178.50		$ 178.50
Warrants issued to U.S. Treasury as part of TARP and loss-sharing agreement | Warrant with the exercise price of $106.10
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities excluded from computation of earnings per common share (in shares)		25,500,000		25,500,000
Antidilutive securities exercise price (in dollars per share)		$ 106.10		$ 106.10		$ 106.10		$ 106.10

[1] Due to rounding, earnings per share on continuing operations and Discontinued operations may not sum to earnings per share on net income.