CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	$ (287)	$ (151)	$ (673)	$ (641)
Income from continuing operations before income taxes	(5,620)	(6,187)	(16,377)	(20,018)
Tax effect	1,733	1,881	4,935	6,037
Income (loss) from continuing operations	(3,887)	(4,306)	(11,442)	(13,981)
Realized gains (losses) on investment securities
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	(162)	(45)	(252)	(286)
Realized gains (losses) on investment securities \| (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	(287)	(151)	(673)	(641)
OTTI gross impairment losses	32	80	283	195
Income from continuing operations before income taxes	(255)	(71)	(390)	(446)
Tax effect	93	26	138	160
Income (loss) from continuing operations	(162)	(45)	(252)	(286)
Debt valuation adjustment (DVA)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	(3)		(6)
Debt valuation adjustment (DVA) \| (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	(5)		(10)
Income from continuing operations before income taxes	(5)		(10)
Tax effect	2		4
Income (loss) from continuing operations	(3)		(6)
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	53	40	115	164
Cash flow hedges \| (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	85	63	185	260
Tax effect	(32)	(23)	(70)	(96)
Income (loss) from continuing operations	53	40	115	164
Cash flow hedges \| (Gain) loss reclassified from AOCI \| Interest rate contracts
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	39	28	96	148
Cash flow hedges \| (Gain) loss reclassified from AOCI \| Foreign exchange contracts
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income from continuing operations before income taxes	46	35	89	112
Pension liability adjustments
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	71	55	186	191
Total tax effect	(31)	(15)	(72)	(70)
Total amounts reclassified out of AOCI, after-tax	40	40	114	121
Prior service cost (benefit)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	(10)	(11)	(31)	(32)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	73	64	208	211
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	8	2	9	12
Foreign currency translation adjustment
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	0	0	0	0
Foreign currency translation adjustment \| (Gain) loss reclassified from AOCI
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Income (loss) from continuing operations	0	0	0	0
Citigroup's accumulated other comprehensive income (loss)
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	(104)	47	(29)	5
Total tax effect	32	(12)	0	(6)
Total amounts reclassified out of AOCI, after-tax	$ (72)	$ 35	$ (29)	$ (1)

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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