REPORTABLE BUSINESS SEGMENTS AND ALL OTHER - Operations by Segment (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) segment	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment				5
Segment Reporting Information [Line Items]
Net interest income	[1]	$ 14,940	$ 13,362	$ 44,127	$ 40,362
Non-interest revenue		7,150	6,847	21,227	20,895
Total revenues, net of interest expense	[1]	22,090	20,209	65,354	61,257
Total operating expenses	[1]	14,290	13,144	41,292	40,497
Provisions for credit losses and for benefits and claims		2,450	2,675	8,045	7,516
Provision (benefits) for income taxes		1,559	1,116	4,085	3,299
Income (loss) from continuing operations		3,791	3,274	11,932	9,945
Identifiable assets		2,642,475		2,642,475		$ 2,352,945
Average loans		725,000	687,000	709,000	682,000
Average deposits		1,382,000	1,311,000	1,343,000	1,316,000
Operating Segments
Segment Reporting Information [Line Items]
Income (loss) from continuing operations		4,568	3,319	12,904	10,116
Operating Segments | Services
Segment Reporting Information [Line Items]
Net interest income		3,823	3,435	10,951	9,977
Non-interest revenue		1,540	1,580	4,363	4,476
Total revenues, net of interest expense		5,363	5,015	15,314	14,453
Compensation expense		647	584	1,920	1,780
Non-compensation expense		2,060	1,991	6,050	6,187
Total operating expenses		2,707	2,575	7,970	7,967
Provisions for credit losses and for benefits and claims		61	127	465	164
Provision (benefits) for income taxes		776	630	2,002	1,626
Income (loss) from continuing operations		1,819	1,683	4,877	4,696
Identifiable assets		627,000		627,000		584,000
Average loans		94,000	87,000	92,000	84,000
Average deposits		893,000	825,000	859,000	812,000
Operating Segments | Markets
Segment Reporting Information [Line Items]
Net interest income		2,251	1,405	7,166	5,149
Non-interest revenue		3,312	3,412	10,262	10,111
Total revenues, net of interest expense		5,563	4,817	17,428	15,260
Compensation expense		972	854	2,982	2,728
Non-compensation expense		2,519	2,485	7,486	7,300
Total operating expenses		3,491	3,339	10,468	10,028
Provisions for credit losses and for benefits and claims		32	141	341	329
Provision (benefits) for income taxes		457	248	1,492	924
Income (loss) from continuing operations		1,583	1,089	5,127	3,979
Identifiable assets		1,182,000		1,182,000		949,000
Average loans		147,000	119,000	137,000	119,000
Average deposits		20,000	19,000	18,000	23,000
Operating Segments | Banking
Segment Reporting Information [Line Items]
Net interest income		562	527	1,583	1,636
Non-interest revenue		1,570	1,070	4,422	3,324
Total revenues, net of interest expense		2,132	1,597	6,005	4,960
Compensation expense		691	676	2,018	2,095
Non-compensation expense		448	440	1,292	1,331
Total operating expenses		1,139	1,116	3,310	3,426
Provisions for credit losses and for benefits and claims		157	177	544	16
Provision (benefits) for income taxes		201	68	513	346
Income (loss) from continuing operations		635	236	1,638	1,172
Identifiable assets		141,000		141,000		143,000
Average loans		81,000	88,000	82,000	89,000
Average deposits		1,000	1,000	0	1,000
Operating Segments | Wealth
Segment Reporting Information [Line Items]
Net interest income		1,332	1,233	3,884	3,261
Non-interest revenue		832	762	2,542	2,228
Total revenues, net of interest expense		2,164	1,995	6,426	5,489
Compensation expense		633	634	1,921	1,907
Non-compensation expense		1,021	960	2,930	2,858
Total operating expenses		1,654	1,594	4,851	4,765
Provisions for credit losses and for benefits and claims		30	33	102	(146)
Provision (benefits) for income taxes		106	85	321	202
Income (loss) from continuing operations		374	283	1,152	668
Identifiable assets		232,000		232,000		224,000
Average loans		151,000	150,000	149,000	150,000
Average deposits		315,000	316,000	311,000	316,000
Operating Segments | USPB
Segment Reporting Information [Line Items]
Net interest income		5,694	5,293	16,706	15,622
Non-interest revenue		(363)	(329)	(1,028)	(717)
Total revenues, net of interest expense		5,331	4,964	15,678	14,905
Compensation expense		531	544	1,622	1,661
Non-compensation expense		1,834	1,832	5,566	5,520
Total operating expenses		2,365	2,376	7,188	7,181
Provisions for credit losses and for benefits and claims		1,842	1,909	5,538	6,428
Provision (benefits) for income taxes		266	157	700	306
Income (loss) from continuing operations		858	522	2,252	990
Identifiable assets		252,000		252,000		252,000
Average loans		220,000	210,000	218,000	207,000
Average deposits		90,000	85,000	90,000	93,000
All Other
Segment Reporting Information [Line Items]
Net interest income		1,278	1,469	3,837	4,717
Non-interest revenue		257	351	841	1,451
Total revenues, net of interest expense		1,535	1,820	4,678	6,168
Total operating expenses		2,168	2,077	6,668	6,868
Provisions for credit losses and for benefits and claims		331	289	1,064	718
Provision (benefits) for income taxes		(263)	(52)	(912)	(29)
Income (loss) from continuing operations		(701)	(494)	(2,142)	(1,389)
Identifiable assets		208,000		208,000		$ 201,000
Average loans		32,000	33,000	31,000	33,000
Average deposits		63,000	65,000	65,000	71,000
Reconciling Items
Segment Reporting Information [Line Items]
Net interest income		0	0	0	0
Non-interest revenue		2	1	(175)	22
Total revenues, net of interest expense		2	1	(175)	22
Total operating expenses		766	67	837	262
Provisions for credit losses and for benefits and claims		(3)	(1)	(9)	7
Provision (benefits) for income taxes		16	(20)	(31)	(76)
Income (loss) from continuing operations		$ (777)	$ (45)	$ (972)	$ (171)

[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.