CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Pre-Tax and After-Tax (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Change in accumulated other comprehensive income (loss), pretax
Balance at the beginning of the period, pretax		$ (32,279)	$ (27,297)	$ (31,060)	$ (27,596)
Change in net unrealized gains (losses) on investment securities, pretax		(1,517)	1,585	(468)	2,288
Cash flow hedges, pretax		118	205	274	386
Benefit plans, pretax		810	(239)	689	(294)
Foreign currency translation adjustment, pretax		(280)	101	(2,583)	(429)
Change, pretax		(869)	1,652	(2,088)	1,951
Balance at the end of the period, pretax		(33,148)	(25,645)	(33,148)	(25,645)
Change in accumulated other comprehensive income (loss), tax effect
Balance at the beginning of the period, tax effect		7,588	8,151	7,844	8,463
Change in net unrealized gains (losses) on investment securities, tax effect		582	(579)	124	(854)
Cash flow hedges, tax effect		(26)	(85)	(96)	(148)
Benefit plans		(232)	95	(201)	117
Foreign currency translation adjustment, tax effect		132	(84)	373	(80)
Change, tax effect		456	(653)	200	(965)
Balance at the end of the period, tax effect		8,044	7,498	8,044	7,498
Change in accumulated other comprehensive income (loss), after-tax
Beginning-of-period balance, net of tax		(24,691)	(19,146)	(23,216)	(19,133)
Change in net unrealized gains (losses) on investment securities, after-tax		(935)	1,006	(344)	1,434
Cash flow hedges, after-tax		92	120	178	238
Change, net of tax	[1]	578	(144)	488	(177)
Foreign currency translation adjustment, after-tax		(148)	17	(2,210)	(509)
Citigroup’s total other comprehensive income (loss)		(413)	999	(1,888)	986
End-of-period balance, net of tax		$ (24,691)	$ (19,146)	$ (23,216)	$ (19,133)	$ (25,104)	$ (18,147)

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