CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	$ (328)	$ (188)	$ (67)
Gross impairment losses	431	323	499
Provision (benefits) for income taxes	4,211	3,528	3,642
Net realized (gains) losses on investments, after-tax	(12,835)	(9,382)	(15,165)
Realized gains (losses) on investment securities
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	(6)	(12)	215
Realized gains (losses) on investment securities | (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	(328)	(188)	(67)
Gross impairment losses	323	188	360
Income from continuing operations before income taxes	(5)	0	293
Provision (benefits) for income taxes	(1)	(12)	(78)
Net realized (gains) losses on investments, after-tax	(6)	(12)	215
Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	17	2	(18)
Debt valuation adjustment (DVA) | (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	23	3	(25)
Provision (benefits) for income taxes	(6)	(1)	7
Net realized (gains) losses on investments, after-tax	17	2	(18)
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	781	1,443	95
Cash flow hedges | (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	1,030	1,901	129
Provision (benefits) for income taxes	(249)	(458)	(34)
Cash flow hedges | (Gain) loss reclassified from AOCI | Interest rate contracts
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	1,027	1,897	125
Cash flow hedges | (Gain) loss reclassified from AOCI | Foreign exchange contracts
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	3	4	4
Benefit plans
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	241	167	161
Total tax effect	(60)	(46)	(45)
Total amounts reclassified out of AOCI, after-tax	181	121	116
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	(17)	(22)	(23)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	256	196	221
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	2	(7)	(37)
Excluded component of fair value hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	(14)	(32)	6
Excluded component of fair value hedges | (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	(18)	(43)	9
Provision (benefits) for income taxes	4	11	(3)
Total amounts reclassified out of AOCI, after-tax	(14)	(32)	6
CTA
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	0	0	384
CTA | (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	0	0	438
Provision (benefits) for income taxes	0	0	(54)
Citigroup's accumulated other comprehensive income (loss)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	1,270	2,028	1,005
Total tax effect	(312)	(506)	(207)
Total amounts reclassified out of AOCI, after-tax	958	1,522	798
Long-duration insurance contracts
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	(1)	0	0
Long-duration insurance contracts | (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	(1)	0	0
Provision (benefits) for income taxes	0	0	0
Total amounts reclassified out of AOCI, after-tax	$ (1)	$ 0	$ 0