GUARANTEES AND COMMITMENTS (Details) (USD $)	Sep. 30, 2011 trust policy Y category	Dec. 31, 2010
Maximum potential amount of future payments
Expire Within One Year	$ 197,900,000,000	$ 178,400,000,000
Expire After One Year	128,800,000,000	121,100,000,000
Total amount outstanding	326,700,000,000	299,500,000,000
Carrying value	2,946,100,000	2,078,000,000
Allowance for credit losses relating to letters of credit and unfunded lending commitments	1,139,000,000	1,066,000,000
Cash collateral available to reimburse losses realized under guarantees and indemnifications	35,000,000,000	35,000,000,000
Securities and other marketable assets held as collateral, the majority of which collateral is held to reimburse losses realized under securities lending indemnifications	57,000,000,000	41,000,000,000
Letters of credit in favor of the Company held as collateral	1,500,000,000	2,000,000,000
Number of trusts funded by the reinsurer	2
Fair value of securities in trusts funded by reinsurer relating to indemnification	4,500,000,000	3,600,000,000
Financial standby letters of credit
Maximum potential amount of future payments
Expire Within One Year	25,900,000,000	26,400,000,000
Expire After One Year	71,900,000,000	68,400,000,000
Total amount outstanding	97,800,000,000	94,800,000,000
Carrying value	468,800,000	225,900,000
Financial standby letters of credit \| Investment grade
Maximum potential amount of future payments
Total amount outstanding	72,000,000,000	58,700,000,000
Financial standby letters of credit \| Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	17,900,000,000	13,200,000,000
Financial standby letters of credit \| Not rated
Maximum potential amount of future payments
Total amount outstanding	7,900,000,000	22,900,000,000
Performance guarantees
Maximum potential amount of future payments
Expire Within One Year	7,300,000,000	9,100,000,000
Expire After One Year	5,000,000,000	4,600,000,000
Total amount outstanding	12,300,000,000	13,700,000,000
Carrying value	47,200,000	35,800,000
Performance guarantees \| Investment grade
Maximum potential amount of future payments
Total amount outstanding	7,000,000,000	7,000,000,000
Performance guarantees \| Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	3,000,000,000	3,400,000,000
Performance guarantees \| Not rated
Maximum potential amount of future payments
Total amount outstanding	2,300,000,000	3,300,000,000
Derivative instruments considered to be guarantees
Maximum potential amount of future payments
Expire Within One Year	8,600,000,000	7,500,000,000
Expire After One Year	8,500,000,000	7,500,000,000
Total amount outstanding	17,100,000,000	15,000,000,000
Carrying value	2,307,700,000	1,445,200,000
Derivative instruments considered to be guarantees \| Not rated
Maximum potential amount of future payments
Total amount outstanding	17,100,000,000	15,000,000,000
Loans sold with recourse
Maximum potential amount of future payments
Expire After One Year	500,000,000	400,000,000
Total amount outstanding	500,000,000	400,000,000
Carrying value	112,700,000	117,300,000
Repurchase reserve for Consumer mortgages representations and warranties	1,076,000,000	969,000,000
Increase in repurchase reserve due to 10% adverse change in significant assumptions	607,000,000
Loans sold with recourse \| Not rated
Maximum potential amount of future payments
Total amount outstanding	500,000,000	400,000,000
Securities lending indemnifications
Maximum potential amount of future payments
Expire Within One Year	84,500,000,000	70,400,000,000
Total amount outstanding	84,500,000,000	70,400,000,000
Securities lending indemnifications \| Not rated
Maximum potential amount of future payments
Total amount outstanding	84,500,000,000	70,400,000,000
Credit card merchant processing
Maximum potential amount of future payments
Expire Within One Year	71,600,000,000	65,000,000,000
Total amount outstanding	71,600,000,000	65,000,000,000
Credit card merchant processing \| Not rated
Maximum potential amount of future payments
Total amount outstanding	71,600,000,000	65,000,000,000
Custody indemnifications and other
Maximum potential amount of future payments
Expire After One Year	42,900,000,000	40,200,000,000
Total amount outstanding	42,900,000,000	40,200,000,000
Carrying value	9,700,000	253,800,000
Custody indemnifications and other \| Investment grade
Maximum potential amount of future payments
Total amount outstanding	42,900,000,000	40,200,000,000
Other guarantees and indemnifications
Maximum potential amount of future payments
Carrying value	2,900,000,000	2,100,000,000
Investment grade
Maximum potential amount of future payments
Total amount outstanding	121,900,000,000	105,900,000,000
Non-investment grade
Maximum potential amount of future payments
Total amount outstanding	20,900,000,000	16,600,000,000
Not rated
Maximum potential amount of future payments
Total amount outstanding	$ 183,900,000,000	$ 177,000,000,000

Represents the allowance for credit losses relating to letters of credit and unfunded lending commitments.

Name:	c_AllowanceForCreditLossesRelatedToLettersOfCreditAndUnfundedLendingCommitments
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the fair value of securities relating to the funding of the trusts by the reinsurer to cover the insurance company's statutory liabilities for long-term care (LTC) Policies.

+ Details

Name:	c_FairValueOfTrustsFundedByInsurer
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	c_GuaranteeObligationsMaximumExposureAbstract
Namespace Prefix:	c
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the maximum potential payments with respect to the entity's guarantees that expire after one year.

+ Details

Name:	c_GuaranteeObligationsMaximumExposureExpireAfterOneYear
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the maximum potential payments with respect to the entity's guarantees that expire within one year.

+ Details

Name:	c_GuaranteeObligationsMaximumExposureExpireWithinOneYear
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the letters of credit in favor of the entity held as collateral to reimburse losses realized under the guarantees.

+ Details

Name:	c_LettersOfCreditReceivedAsCollateral
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the number of trusts funded by the reinsurer.

+ Details

Name:	c_NumberOfTrustFundedByReinsurer
Namespace Prefix:	c
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the repurchase reserve created for consumer mortgages, representations and warranties.

+ Details

Name:	c_RepurchaseReserveConsumerMortgagesRepresentationsAndWarranties
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The hypothetical financial impact of a 10 percent adverse change in significant assumptions on the repurchase reserve.

+ Details

Name:	c_SensitivityAnalysisOfRepurchaseReserveImpactOf10PercentAdverseChangeInSignificantAssumptions
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 2

-Article 7

+ Details

Name:	us-gaap_CashCollateralForBorrowedSecurities
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph c

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph b

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability

+ References

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Chapter 4

-Paragraph 49

-IssueDate 2006-05-01

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 17

-Subparagraph a(3)

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 15

-Subparagraph a, b, c, d

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 91

+ Details

Name:	us-gaap_SecuritiesReceivedAsCollateral
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant