CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Schedule of Pre-Tax and After-Tax (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period			$ 202,672
Balance, end of period	$ 199,117	$ 201,610	199,117	$ 201,610
Change in net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(850)	(374)	(8,464)	(3,439)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	270	95	2,106	901
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(6,392)	1,061	(614)	3,320
Total other comprehensive income	(580)	(279)	(6,358)	(2,538)
Balance, end of period	(6,972)	782	(6,972)	782
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	1,159	(107)	4,800	(256)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(287)	25	(1,168)	70
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	1,573	(1,523)	(1,187)	(1,419)
Total other comprehensive income	872	(82)	3,632	(186)
Balance, end of period	2,445	(1,605)	2,445	(1,605)
Hedges
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	10	(67)	(47)	(47)
Total other comprehensive income	30	8	87	(12)
Balance, end of period	40	(59)	40	(59)
Benefit plans
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(4)	175	100	1,166
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	41	(40)	19	(230)
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(5,770)	(6,063)	(5,852)	(6,864)
Total other comprehensive income	37	135	119	936
Balance, end of period	(5,733)	(5,928)	(5,733)	(5,928)
Foreign currency translation adjustment
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(2,238)	(1,325)	(3,720)	(2,217)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(161)	13	(323)	154
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(32,810)	(29,392)	(31,166)	(28,641)
Total other comprehensive income	(2,399)	(1,312)	(4,043)	(2,063)
Balance, end of period	(35,209)	(30,704)	(35,209)	(30,704)
Citigroup's accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss), pretax
Balance, beginning of period, pretax	(53,566)	(41,087)	(45,383)	(36,992)
Other comprehensive income (loss), pretax	(2,918)	(1,884)	(11,101)	(5,979)
Balance, end of period, pretax	(56,484)	(42,971)	(56,484)	(42,971)
Change in accumulated other comprehensive income (loss), tax effect
Balance, beginning of period, tax effect	8,071	5,967	6,618	4,934
Other comprehensive income (loss), tax effect	115	153	1,568	1,186
Balance, end of period, tax effect	8,186	6,120	8,186	6,120
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period	(45,495)	(35,120)	(38,765)	(32,058)
Total other comprehensive income	(2,803)	(1,731)	(9,533)	(4,793)
Balance, end of period	(48,298)	(36,851)	(48,298)	(36,851)
Cash flow hedges | Hedges
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	(1,025)	(265)	(3,933)	(1,219)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	262	64	963	289
Change in accumulated other comprehensive income (loss), after-tax
Total other comprehensive income	(763)	(201)	(2,970)	(930)
Fair value hedges | Hedges
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax	40	12	116	(14)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect	(10)	(4)	(29)	2
Change in accumulated other comprehensive income (loss), after-tax
Total other comprehensive income	$ 30	$ 8	$ 87	$ (12)