EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share
Income from continuing operations before attribution of noncontrolling interests		$ 3,274			$ 3,585	$ 9,945	$ 11,189
Noncontrolling interests		35			41	117	122
Net income from continuing operations (for EPS purposes)		3,239			3,544	9,828	11,067
Income (loss) from discontinued operations, net of taxes		(1)			2	(2)	0
Citigroup’s net income		3,238			3,546	9,826	11,067
Less: Preferred dividends		277			333	798	898
Net income available to common shareholders		2,961			3,213	9,028	10,169
Less: Dividends and undistributed earnings allocated to employee restricted and deferred shares with rights to dividends, and other relevant items, applicable to basic EPS		56			53	133	121
Net income allocated to common shareholders for basic EPS		$ 2,905			$ 3,160	$ 8,895	$ 10,048
Weighted-average common shares outstanding applicable to basic EPS (in shares)		1,899.9			1,924.4	1,906.0	1,936.9
Basic earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 1.53			$ 1.64	$ 4.67	$ 5.19
Discontinued operations (in dollars per share)	[1]	0			0	0	0
Net income (in dollars per share)	[1]	$ 1.53			$ 1.64	$ 4.67	$ 5.19
Add back: Dividends allocated to employee restricted and deferred shares with rights to dividends that are forfeitable		$ 20			$ 16	$ 54	$ 42
Net income allocated to common shareholders for diluted EPS		$ 2,925			$ 3,176	$ 8,949	$ 10,090
Effect of dilutive securities
Other employee plans (in shares)		40.4			27.3	37.1	24.6
Adjusted weighted-average common shares outstanding applicable to diluted EPS (in shares)		1,940.3			1,951.7	1,943.1	1,961.5
Diluted earnings per share
Income from continuing operations (in dollars per share)	[1]	$ 1.51			$ 1.63	$ 4.61	$ 5.14
Discontinued operations (in dollars per share)	[1]	0			0	0	0
Net income (in dollars per share)	[1]	$ 1.51			$ 1.63	$ 4.61	$ 5.14
Excise tax			$ 14
Income allocated to employees with no rights to dividends		$ 40
Series M
Diluted earnings per share
Issuance costs		11
Series U
Diluted earnings per share
Issuance costs		$ 5
Series D
Diluted earnings per share
Issuance costs			$ 8
Series J
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.