EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Income from continuing operations before attribution of noncontrolling interests		$ 4,306	$ 2,916	$ 13,981	$ 7,121
Less: Noncontrolling interests from continuing operations		5	59	65	154
Net income from continuing operations (for EPS purposes)		4,301	2,857	13,916	6,967
Income (loss) from discontinued operations, net of taxes		(10)	(16)	(9)	(1)
Citigroup’s net income		4,291	2,841	13,907	6,966
Less: Preferred dividends		174	128	504	352
Net income available to common shareholders		4,117	2,713	13,403	6,614
Less: Dividends and undistributed earnings allocated to employee restricted and deferred shares with nonforfeitable rights to dividends, applicable to basic EPS		56	44	182	108
Net income allocated to common shareholders for basic and diluted EPS		$ 4,061	$ 2,669	$ 13,221	$ 6,506
Weighted-average common shares outstanding applicable to basic EPS		2,993.3	3,029.5	3,015.8	3,033.5
Effect of dilutive securities
Options (in shares)		3.4	5.1	4.4	5.0
Other employee plans (in shares)		0.2	0.2	0.2	0.3
Convertible securities (in shares)		0.0	0.0	0.0	0.0
Adjusted weighted-average common shares outstanding applicable to diluted EPS (in shares)		2,996.9	3,034.8	3,020.4	3,038.8
Basic earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 1.36	$ 0.89	$ 4.39	$ 2.14
Discontinued operations (in dollars per share)	[1]	0.00	(0.01)	0.00	0.00
Net income (in dollars per share)	[1]	1.36	0.88	4.38	2.14
Diluted earnings per share
Income from continuing operations (in dollars per share)	[1]	1.36	0.88	4.38	2.14
Discontinued operations (in dollars per share)	[1]	0.00	(0.01)	0.00	0.00
Net income (in dollars per share)	[1]	$ 1.35	$ 0.88	4.38	2.14
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)		0.9	1.9
Antidilutive securities exercise price (in dollars per share)		$ 201.01	$ 157.90	$ 201.01	$ 157.90
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)		21.0	21.0	21.0	21.0
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)		25.5	25.5	25.5	25.5
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.