OPERATING SEGMENTS - Operations by Segment (Details) $ in Millions		3 Months Ended
		Mar. 31, 2025 USD ($) segment	Mar. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment		5
Segment Reporting Information [Line Items]
Net interest income	[1]	$ 14,012	$ 13,507
Non-interest revenue		7,584	7,509
Total revenues, net of interest expense(1)	[1]	21,596	21,016
Total operating expenses	[1]	13,425	14,107
Provisions for credit losses and for benefits and claims	[1]	2,723	2,365
Provision (benefits) for income taxes		1,340	1,136
Income (loss) from continuing operations		4,108	3,408
Identifiable assets		2,571,514		$ 2,352,945
Average loans		691,000	679,000
Average deposits		1,305,000	1,326,000
Operating Segments
Segment Reporting Information [Line Items]
Income (loss) from continuing operations		4,123	3,502
Operating Segments | Services
Segment Reporting Information [Line Items]
Net interest income		3,498	3,317
Non-interest revenue		1,391	1,446
Total revenues, net of interest expense(1)		4,889	4,763
Compensation expense		632	624
Non-compensation expense		1,952	2,039
Total operating expenses		2,584	2,663
Provisions for credit losses and for benefits and claims		51	64
Provision (benefits) for income taxes		644	521
Income (loss) from continuing operations		1,610	1,515
Identifiable assets		589,000		584,000
Average loans		87,000	82,000
Average deposits		826,000	808,000
Operating Segments | Markets
Segment Reporting Information [Line Items]
Net interest income		2,013	1,706
Non-interest revenue		3,973	3,651
Total revenues, net of interest expense(1)		5,986	5,357
Compensation expense		1,018	978
Non-compensation expense		2,450	2,406
Total operating expenses		3,468	3,384
Provisions for credit losses and for benefits and claims		201	199
Provision (benefits) for income taxes		522	353
Income (loss) from continuing operations		1,795	1,421
Identifiable assets		1,165,000		949,000
Average loans		128,000	120,000
Average deposits		15,000	24,000
Operating Segments | Banking
Segment Reporting Information [Line Items]
Net interest income		491	582
Non-interest revenue		1,461	1,154
Total revenues, net of interest expense(1)		1,952	1,736
Compensation expense		632	724
Non-compensation expense		402	455
Total operating expenses		1,034	1,179
Provisions for credit losses and for benefits and claims		214	(129)
Provision (benefits) for income taxes		162	159
Income (loss) from continuing operations		542	527
Identifiable assets		147,000		143,000
Average loans		82,000	89,000
Average deposits		0	1,000
Operating Segments | USPB
Segment Reporting Information [Line Items]
Net interest income		5,541	5,226
Non-interest revenue		(313)	(117)
Total revenues, net of interest expense(1)		5,228	5,109
Compensation expense		554	564
Non-compensation expense		1,888	1,886
Total operating expenses		2,442	2,450
Provisions for credit losses and for benefits and claims		1,811	2,204
Provision (benefits) for income taxes		230	108
Income (loss) from continuing operations		745	347
Identifiable assets		244,000		252,000
Average loans		216,000	204,000
Average deposits		89,000	100,000
Operating Segments | Wealth
Segment Reporting Information [Line Items]
Net interest income		1,274	981
Non-interest revenue		822	706
Total revenues, net of interest expense(1)		2,096	1,687
Compensation expense		669	646
Non-compensation expense		970	990
Total operating expenses		1,639	1,636
Provisions for credit losses and for benefits and claims		98	(170)
Provision (benefits) for income taxes		75	46
Income (loss) from continuing operations		284	175
Identifiable assets		224,000		224,000
Average loans		147,000	150,000
Average deposits		310,000	316,000
All Other
Segment Reporting Information [Line Items]
Net interest income		1,195	1,695
Non-interest revenue		250	681
Total revenues, net of interest expense(1)		1,445	2,376
Total operating expenses		2,224	2,685
Provisions for credit losses and for benefits and claims		359	186
Provision (benefits) for income taxes		(285)	(12)
Income (loss) from continuing operations		(853)	(483)
Identifiable assets		203,000		$ 201,000
Average loans		31,000	34,000
Average deposits		65,000	77,000
Reconciling Items
Segment Reporting Information [Line Items]
Net interest income		0	0
Non-interest revenue		0	(12)
Total revenues, net of interest expense(1)		0	(12)
Total operating expenses		34	110
Provisions for credit losses and for benefits and claims		(11)	11
Provision (benefits) for income taxes		(8)	(39)
Income (loss) from continuing operations		$ (15)	$ (94)

[1]     Effective January 1, 2025, certain transaction processing fees paid by Citi, primarily to credit card networks, which were previously presented within Other operating expenses, are presented as contra-revenue within Commissions and fees reported in Non-interest revenue. Prior periods were conformed to reflect this change in presentation.