CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassification out of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Realized (gains) losses on sales of investments	$ (192)	$ (186)
Income from continuing operations before income taxes	(5,981)	(4,987)
Provision (benefits) for income taxes	1,863	1,479
Income (loss) from continuing operations	(4,118)	(3,508)
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	(114)	8
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	(192)	(186)
OTTI gross impairment losses	12	203
Income from continuing operations before income taxes	(180)	17
Provision (benefits) for income taxes	66	(9)
Income (loss) from continuing operations	(114)	8
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	(5)	1
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	(8)	1
Income from continuing operations before income taxes	(8)	1
Provision (benefits) for income taxes	3	0
Income (loss) from continuing operations	(5)	1
Cash flow hedges
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, after-tax	(26)	26
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	(41)	42
Provision (benefits) for income taxes	15	(16)
Income (loss) from continuing operations	(26)	26
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	(44)	16
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	3	26
Pension liability adjustments
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	57	54
Total tax effect	(20)	(19)
Total amounts reclassified out of AOCI, after-tax	37	35
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)	(10)
Net actuarial loss
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	67	66
Curtailment/settlement impact
Pretax and after-tax amounts reclassified out of accumulated other comprehensive income (loss)
Total amounts reclassified out of AOCI, pretax	0	(2)
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	(147)	0
Foreign currency translation adjustment \| (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	(232)	0
Provision (benefits) for income taxes	85	0
Income (loss) from continuing operations	(147)	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	(404)	114
Total tax effect	149	(44)
Total amounts reclassified out of AOCI, after-tax	$ (255)	$ 70

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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