CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses	$ (52)	$ (117)	$ (74)	$ (655)
Gross impairment losses	91	30	277	112
Tax effect	879	1,193	3,002	4,680
Income (loss) from continuing operations	(3,515)	(4,669)	(12,629)	(18,839)
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	15	(75)	132	(437)
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	(52)	(117)	(74)	(655)
Gross impairment losses	74	21	254	99
Income from continuing operations before income taxes	22	(96)	180	(556)
Tax effect	(7)	21	(48)	119
Income (loss) from continuing operations	15	(75)	132	(437)
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	(2)	56	(3)	109
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	(3)	72	(4)	141
Tax effect	1	(16)	1	(32)
Income (loss) from continuing operations	(2)	56	(3)	109
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	107	(203)	(261)	(612)
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	142	(268)	(341)	(806)
Tax effect	(35)	65	80	194
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	141	(269)	(344)	(809)
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	3	3
Benefit plan adjustments
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	43	70	127	220
Total tax effect	(11)	(19)	(34)	(57)
Total amounts reclassified out of AOCI, after-tax	32	51	93	163
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	(6)	(5)	(17)	(17)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	49	74	177	232
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	0	1	(33)	5
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	(1)	1	6	2
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	(1)	1	9	2
Tax effect	0	0	(3)	0
Total amounts reclassified out of AOCI, after-tax	(1)	1	6	2
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	24	13	369	13
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	26	20	423	20
Tax effect	(2)	(7)	(54)	(7)
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	229	(201)	394	(979)
Total tax effect	(54)	44	(58)	217
Total amounts reclassified out of AOCI, after-tax	$ 175	$ (157)	$ 336	$ (762)