CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Pre-Tax and After-Tax (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Change in accumulated other comprehensive income (loss), pretax
Balance at the beginning of the period, pretax	$ (31,060)		$ (27,596)		$ (27,596)
Change in net unrealized gains (losses) on investment securities, pretax	1,048		703
Cash flow hedges, pretax	156		181
Benefit plans, pretax	(121)		(55)
Foreign currency translation adjustment, pretax	(2,302)		(530)
Change, pretax	(1,219)		299
Balance at the end of the period, pretax	(32,279)		(27,297)		(31,060)
Change in accumulated other comprehensive income (loss), tax effect
Balance at the beginning of the period, tax effect	7,844		8,463		8,463
Change in net unrealized gains (losses) on investment securities, tax effect	(457)		(275)
Cash flow hedges, tax effect	(70)		(63)
Benefit plans	31		22		660
Foreign currency translation adjustment, tax effect	240		4
Change, tax effect	(256)		(312)
Balance at the end of the period, tax effect	7,588		8,151		7,844
Change in accumulated other comprehensive income (loss), after-tax
Beginning-of-period balance, net of tax	(23,216)		(19,133)		(19,133)
Change in net unrealized gains (losses) on investment securities, after-tax	591		428
Cash flow hedges, after-tax	86		118
Change, net of tax	(90)	[1]	(33)	[1]	(1,170)
Foreign currency translation adjustment, after-tax	(2,062)		(526)
Citigroup’s total other comprehensive income (loss)	(1,475)		(13)
End-of-period balance, net of tax	$ (24,691)		$ (19,146)		$ (23,216)

[1] Reflects adjustments based on the actuarial valuations of the Company’s significant pension and postretirement plans, including changes in the mortality assumptions at March 31, 2015, and amortization of amounts previously recognized in Accumulated other comprehensive income (loss). See Note 8 to the Consolidated Financial Statements.