GOODWILL AND INTANGIBLE ASSETS - Components of Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	$ 15,098	$ 15,116
Accumulated amortization of Intangible assets (excluding MSRs)	10,532	10,060
Net carrying amount of Intangible assets (excluding MSRs)	4,566	5,056
Gross carrying amount, Mortgage servicing rights (MSRs)	1,845	2,718
Mortgage servicing rights (MSRs)	1,845c_MortgageServicingRightsMSR	2,718c_MortgageServicingRightsMSR
Gross carrying amount of Intangible assets	16,943	17,834
Accumulated amortization of Intangible assets	10,532	10,060
Net carrying amount of Intangible assets, balance at end of period	6,411	7,774
Intangible assets amortization expense	756us-gaap_AmortizationOfIntangibleAssets	808us-gaap_AmortizationOfIntangibleAssets	856us-gaap_AmortizationOfIntangibleAssets
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2015	659
2016	634
2017	938
2018	411
2019	368
Indefinite-lived intangible assets
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	290	323
Accumulated amortization of Intangible assets (excluding MSRs)	0	0
Net carrying amount of Intangible assets (excluding MSRs)	290	323
Purchased credit card relationships
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	7,626	7,552
Accumulated amortization of Intangible assets (excluding MSRs)	6,294	6,006
Net carrying amount of Intangible assets (excluding MSRs)	1,332	1,546
Core deposit intangibles
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	1,153	1,255
Accumulated amortization of Intangible assets (excluding MSRs)	1,021	1,052
Net carrying amount of Intangible assets (excluding MSRs)	132	203
Other customer relationships
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	579	675
Accumulated amortization of Intangible assets (excluding MSRs)	331	389
Net carrying amount of Intangible assets (excluding MSRs)	248	286
Present value of future profits
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	233	238
Accumulated amortization of Intangible assets (excluding MSRs)	154	146
Net carrying amount of Intangible assets (excluding MSRs)	79	92
Other
Finite and Indefinite-lived Intangible Assets [Line Items]
Gross carrying amount of Intangible assets (excluding MSRs)	5,217	5,073
Accumulated amortization of Intangible assets (excluding MSRs)	2,732	2,467
Net carrying amount of Intangible assets (excluding MSRs)	$ 2,485	$ 2,606

Name:	c_FiniteAndIndefiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	c_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Sum of the carrying amounts of all intangible assets, excluding goodwill and excluding mortgage servicing rights, as of the balance sheet date, net of accumulated amortization and impairment charges.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRights
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the accumulated amortization of all intangible assets, excluding goodwill and mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsAccumulatedAmortization
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the gross carrying amounts of all intangible assets, excluding goodwill and mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsExcludingMortgageServicingRightsGrossCarryingAmount
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the sum of the carrying amounts of all intangible assets excluding goodwill but including mortgage servicing rights, as of the balance sheet date that is net of accumulated amortization and impairment charges.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsIncludingMortgageServicingRights
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the accumulated amortization of all intangible assets excluding goodwill but including mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsIncludingMortgageServicingRightsAccumulatedAmortization
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the gross carrying amount of intangible assets excluding goodwill but including mortgage servicing rights (MSRs), as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_IntangibleAssetsIncludingMortgageServicingRightsGrossCarryingAmount
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of mortgage servicing rights (MSRs) as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_MortgageServicingRightsMSR
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the gross carrying amount of mortgage servicing rights (MSRs) as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	c_MortgageServicingRightsMSRGrossCarryingAmount
Namespace Prefix:	c_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_OtherCustomerRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_OtherFiniteLivedIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_PresentValueOfFutureProfitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=c_PurchasedCreditCardRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoreDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_IndefinitelivedIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: