EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Income from continuing operations before attribution of noncontrolling interests		$ 4,325	$ 7,977
Noncontrolling interests		17	33
Net income from continuing operations (for EPS purposes)		4,308	7,944
Income (loss) from discontinued operations, net of taxes		(2)	(2)
Citigroup’s net income		4,306	7,942
Less: Preferred dividends		279	292
Net income available to common shareholders		4,027	7,650
Less: Dividends and undistributed earnings allocated to employee restricted and deferred shares with rights to dividends, applicable to basic EPS		25	66
Net income allocated to common shareholders for basic EPS		$ 4,002	$ 7,584
Weighted-average common shares outstanding applicable to basic EPS (in shares)		1,971.7	2,082.0
Basic earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 2.03	$ 3.64
Discontinued operations (in dollars per share)	[1]	0	0
Net income (in dollars per share)	[1]	$ 2.03	$ 3.64
Add back: Dividends allocated to employee restricted and deferred shares with rights to dividends that are forfeitable		$ 8	$ 7
Net income allocated to common shareholders for diluted EPS		$ 4,010	$ 7,591
Effect of dilutive securities
Options (in shares)		0.0	0.1
Other employee plans (in shares)		16.5	14.5
Adjusted weighted-average common shares outstanding applicable to diluted EPS (in shares)		1,988.2	2,096.6
Diluted earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 2.02	$ 3.62
Discontinued operations (in dollars per share)	[1]	0	0
Net income (in dollars per share)	[1]	$ 2.02	$ 3.62

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