EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended
		Feb. 28, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019
Earnings Per Share [Abstract]
Income from continuing operations before attribution of noncontrolling interests			$ 4,737	$ 4,649
Noncontrolling interests			25	22
Net income from continuing operations (for EPS purposes)			4,712	4,627
Loss from discontinued operations, net of taxes			(2)	(7)
Citigroup’s net income			4,710	4,620
Less: Preferred dividends			262	272
Net income available to common shareholders			4,448	4,348
Less: Dividends and undistributed earnings allocated to employee restricted and deferred shares with nonforfeitable rights to dividends, applicable to basic EPS			59	51
Net income allocated to common shareholders for basic EPS			4,389	4,297
Net income allocated to common shareholders for diluted EPS			$ 4,389	$ 4,297
Weighted-average common shares outstanding applicable to basic EPS (in shares)			2,340.4	2,561.6
Effect of dilutive securities
Options (in shares)			0.1	0.1
Other employee plans (in shares)			1.9	1.3
Adjusted weighted-average common shares outstanding applicable to diluted EPS (in shares)			2,342.4	2,563.0
Basic earnings per share
Income from continuing operations (in dollars per share)	[1]		$ 1.88	$ 1.68
Discontinued operations (in dollars per share)	[1]		0	0
Net income (in dollars per share)	[1]		1.88	1.68
Diluted earnings per share
Income from continuing operations (in dollars per share)	[1]		1.87	1.68
Discontinued operations (in dollars per share)	[1]		0	0
Net income (in dollars per share)	[1]		$ 1.87	1.68
Weighted-average options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive securities exercise price (in dollars per share)				$ 149.41
Antidilutive securities excluded from computation of earnings per common share (in shares)				0.5
Forecast
Antidilutive Securities Excluded from Computation of Earnings Per Share
Distribution of preferred dividends					$ 846
Preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Treasury stock acquired			$ 480	$ 97
Preferred stock | Series AA
Antidilutive Securities Excluded from Computation of Earnings Per Share
Number of shares redeemed			19.2
Treasury stock acquired		$ 480

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