CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Schedule of Pre-Tax and After-Tax (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period			$ 202,672
Balance, end of period	$ 199,626	$ 202,910	199,626	$ 202,910
Change in net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(1,990)	(638)	(7,614)	(3,065)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	489	164	1,836	806
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(4,891)	1,535	(614)	3,320
Total other comprehensive income	(1,501)	(474)	(5,778)	(2,259)
Balance, end of period	(6,392)	1,061	(6,392)	1,061
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	2,592	(110)	3,642	(148)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(625)	48	(882)	44
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(394)	(1,461)	(1,187)	(1,419)
Total other comprehensive income	1,967	(62)	2,760	(104)
Balance, end of period	1,573	(1,523)	1,573	(1,523)
Hedges
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	1	(57)	(47)	(47)
Total other comprehensive income	9	(10)	57	(20)
Balance, end of period	10	(67)	10	(67)
Benefit plans
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(73)	84	104	991
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(16)	3	(22)	(190)
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(5,681)	(6,150)	(5,852)	(6,864)
Total other comprehensive income	(89)	87	82	801
Balance, end of period	(5,770)	(6,063)	(5,770)	(6,063)
Foreign currency translation adjustment
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(1,414)	445	(1,483)	(894)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(216)	78	(161)	143
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(31,180)	(29,915)	(31,166)	(28,641)
Total other comprehensive income	(1,630)	523	(1,644)	(751)
Balance, end of period	(32,810)	(29,392)	(32,810)	(29,392)
Citigroup's accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss), pretax
Balance, beginning of period, pretax	(51,807)	(40,631)	(45,383)	(36,992)
Other comprehensive income (loss), pretax	(1,759)	(456)	(8,183)	(4,095)
Balance, end of period, pretax	(53,566)	(41,087)	(53,566)	(41,087)
Change in accumulated other comprehensive income (loss), tax effect
Balance, beginning of period, tax effect	8,222	5,620	6,618	4,934
Other comprehensive income (loss), tax effect	(151)	347	1,453	1,033
Balance, end of period, tax effect	8,071	5,967	8,071	5,967
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(43,585)	(35,011)	(38,765)	(32,058)
Total other comprehensive income	(1,910)	(109)	(6,730)	(3,062)
Balance, end of period	(45,495)	(35,120)	(45,495)	(35,120)
Cash flow hedges | Hedges
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(886)	(224)	(2,908)	(953)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	220	51	701	224
Change in accumulated other comprehensive income (loss), after-tax
Total other comprehensive income	(666)	(173)	(2,207)	(729)
Fair value hedges | Hedges
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	12	(13)	76	(26)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(3)	3	(19)	6
Change in accumulated other comprehensive income (loss), after-tax
Total other comprehensive income	$ 9	$ (10)	$ 57	$ (20)