CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses	$ (49)	$ 58	$ (121)	$ (22)
Gross impairment losses	71	96	157	186
Tax effect	1,090	1,182	2,621	2,123
Income (loss) from continuing operations	(2,952)	(4,789)	(7,604)	(9,114)
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	(7)	111	(26)	117
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	(49)	58	(121)	(22)
Gross impairment losses	43	90	94	180
Income from continuing operations before income taxes	(6)	148	(27)	158
Tax effect	(1)	(37)	1	(41)
Income (loss) from continuing operations	(7)	111	(26)	117
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	(6)	(1)	(4)	(1)
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	(7)	(1)	(4)	(1)
Tax effect	1	0	0	0
Income (loss) from continuing operations	(6)	(1)	(4)	(1)
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	377	(151)	732	(368)
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	496	(198)	966	(483)
Tax effect	(119)	47	(234)	115
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	495	(199)	964	(485)
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	1	1	2	2
Benefit plan adjustments
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	47	236	85	84
Total tax effect	(13)	(54)	(23)	(23)
Total amounts reclassified out of AOCI, after-tax	34	182	62	61
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	(5)	(5)	(11)	(11)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	51	58	100	128
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	1	183	(4)	(33)
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	(10)	5	(14)	7
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	(13)	7	(19)	10
Tax effect	3	(2)	5	(3)
Total amounts reclassified out of AOCI, after-tax	(10)	5	(14)	7
Foreign currency translation adjustment
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	0	345	0	345
Foreign currency translation adjustment | (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	397	0	397
Tax effect	0	(52)	0	(52)
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	0	0	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	0	0	0	0
Tax effect	0	0	0	0
Total amounts reclassified out of AOCI, after-tax	0	0	0	0
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	517	589	1,001	165
Total tax effect	(129)	(98)	(251)	(4)
Total amounts reclassified out of AOCI, after-tax	$ 388	$ 491	$ 750	$ 161