CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Schedule of Pre-Tax and After-Tax (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		$ 226,143
Balance, end of period		229,153	$ 228,761
AOCI		(30,917)		$ (32,381)
Retained earnings		149,731		146,477
Net unrealized gains (losses) on investment securities
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax		346	3,224
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect		(126)	(1,190)
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		(799)	(907)
Adjustment to opening balance						$ 0
Adjusted balance, beginning of period						(907)
Total other comprehensive income		220	2,034
Balance, end of period		(579)	1,127
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax		(95)	307
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect		35	(114)
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		(352)	0
Adjustment to opening balance						(15)
Adjusted balance, beginning of period						(15)
Total other comprehensive income		(60)	193
Balance, end of period		(412)	178
Cash flow hedges
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax		1	481
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect		(3)	(164)
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		(560)	(617)
Adjustment to opening balance						0
Adjusted balance, beginning of period						(617)
Total other comprehensive income		(2)	317
Balance, end of period		(562)	(300)
Benefit plans
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax		(2)	(727)
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect		(10)	262
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		(5,164)	(5,116)
Adjustment to opening balance						0
Adjusted balance, beginning of period						(5,116)
Total other comprehensive income		(12)	(465)
Balance, end of period		(5,176)	(5,581)
Foreign currency translation adjustment
Change in accumulated other comprehensive income (loss), pretax
Other comprehensive income (loss), pretax		1,468	513
Change in accumulated other comprehensive income (loss), tax effect
Other comprehensive income (loss), tax effect		(150)	141
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		(25,506)	(22,704)
Adjustment to opening balance						0
Adjusted balance, beginning of period						(22,704)
Total other comprehensive income		1,318	654
Balance, end of period		(24,188)	(22,050)
Citigroup's accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss), pretax
Balance, beginning of period, pretax		(42,035)	(38,440)
Adjustment to opening balance, pretax						(26)
Adjusted balance, beginning of period, pretax						(38,466)
Other comprehensive income (loss), pretax		1,718	3,798
Balance, end of period, pretax		(40,317)	(34,668)
Change in accumulated other comprehensive income (loss), tax effect
Balance, beginning of period, tax effect		9,654	9,096
Adjustment to opening balance, tax effect						11
Adjusted balance, beginning of period, tax effect						9,107
Other comprehensive income (loss), tax effect		(254)	(1,065)
Balance, end of period, tax effect		9,400	8,042
Change in accumulated other comprehensive income (loss), after-tax
Balance, beginning of period		(32,381)	(29,344)
Adjustment to opening balance	[1]			0		(15)
Adjusted balance, beginning of period				$ (32,381)		$ (29,359)
Total other comprehensive income		1,464	2,733
Balance, end of period		$ (30,917)	$ (26,626)
Accounting Standards Update 2016-01 | New Accounting Pronouncement, Early Adoption, Effect
Change in accumulated other comprehensive income (loss), after-tax
AOCI					$ (15)
Retained earnings					$ 15

[1] See Note 1 to the Consolidated Financial Statements for additional details.