EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share
Income from continuing operations before attribution of noncontrolling interests		$ 3,408	$ 4,652
Noncontrolling interests		36	45
Net income from continuing operations (for EPS purposes)		3,372	4,607
Income (loss) from discontinued operations, net of taxes		(1)	(1)
Citigroup’s net income		3,371	4,606
Less: Preferred dividends		279	277
Net income available to common shareholders		3,092	4,329
Less: Dividends and undistributed earnings allocated to employee restricted and deferred shares with rights to dividends, and other relevant items, applicable to basic EPS		45	34
Net income allocated to common shareholders for basic EPS		$ 3,047	$ 4,295
Weighted-average common shares outstanding applicable to basic EPS (in shares)		1,910.4	1,943.5
Basic earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 1.60	$ 2.21
Discontinued operations (in dollars per share)	[1]	0	0
Net income (in dollars per share)	[1]	$ 1.59	$ 2.21
Add back: Dividends allocated to employee restricted and deferred shares with rights to dividends that are forfeitable		$ 15	$ 11
Net income allocated to common shareholders for diluted EPS		$ 3,062	$ 4,306
Effect of dilutive securities
Other employee plans (in shares)		32.8	20.6
Adjusted weighted-average common shares outstanding applicable to diluted EPS (in shares)		1,943.2	1,964.1
Diluted earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 1.58	$ 2.19
Discontinued operations (in dollars per share)	[1]	0	0
Net income (in dollars per share)	[1]	$ 1.58	$ 2.19
Series A Preferred Stock and Series B Preferred Stock
Diluted earnings per share
Issuance costs				$ 12

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