CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Pre-Tax and After-Tax (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Change in accumulated other comprehensive income (loss), pretax
Balance at the beginning of the period, pretax		$ (33,148)	$ (25,645)	$ (31,060)	$ (27,596)
Change in net unrealized gains (losses) on investment securities, pretax		821	(321)	353	1,967
Cash flow hedges, pretax		322	45	596	431
Benefit plans, pretax		(545)	107	144	(187)
Foreign currency translation adjustment, pretax		(2,792)	(2,094)	(5,375)	(2,523)
Change, pretax		(2,194)	(2,263)	(4,282)	(312)
Balance at the end of the period, pretax		(35,342)	(27,908)	(35,342)	(27,908)
Change in accumulated other comprehensive income (loss), tax effect
Balance at the beginning of the period, tax effect		8,044	7,498	7,844	8,463
Change in net unrealized gains (losses) on investment securities, tax effect		(310)	114	(186)	(740)
Cash flow hedges, tax effect		(133)	(17)	(229)	(165)
Benefit plans		185	(36)	(16)	81
Foreign currency translation adjustment, tax effect		299	373	672	293
Change, tax effect		41	434	241	(531)
Balance at the end of the period, tax effect		8,085	7,932	8,085	7,932
Change in accumulated other comprehensive income (loss), after-tax
Beginning-of-period balance, net of tax		(25,104)	(18,147)	(23,216)	(19,133)
Change in net unrealized gains (losses) on investment securities, after-tax		511	(207)	167	1,227
Cash flow hedges, after-tax		189	28	367	266
Change, net of tax	[1]	(360)	71	128	(106)
Foreign currency translation adjustment, after-tax		(2,493)	(1,721)	(4,703)	(2,230)
Citigroup’s total other comprehensive income (loss)		(2,153)	(1,829)	(4,041)	(843)
End-of-period balance, net of tax		$ (25,104)	$ (18,147)	$ (23,216)	$ (19,133)	$ (27,257)	$ (19,976)

[1] Reflects adjustments based on the actuarial valuations of the Company’s significant pension and postretirement plans, including changes in the mortality assumptions at September 30, 2015, and amortization of amounts previously recognized in Accumulated other comprehensive income (loss). See Note 8 to the Consolidated Financial Statements.