Changes in the fair value of assets and liabilities related to significant unobservable inputs (Level 3).

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

- Definition

This element represents the transfers from Level 3 of assets measured at fair value on a recurring basis using unobservable inputs, which have taken place during the period.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsAssetsTransferredFromLevel3ToLevel2
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the transfers into Level 3 of assets measured at fair value on a recurring basis using unobservable inputs, which have taken place during the period.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsAssetsTransferredToLevel3FromLevel2
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the increase (decrease) in the balance of credit derivatives classified as Level 3 assets.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsCreditDerivativesIncreaseDecreaseInLevel3
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the increase (decrease) in the balance of investments, due to paydowns and sales.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsInvestmentsDueToPaydownsAndSales
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the increase (decrease) in the balance of long-term debt related toscheduled termination of a structured transaction at fair value on a recurring basis using unobservable inputs, which have taken place during the period.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsLongTermDebtScheduledTerminationOfStructuredTransactionIncreaseDecreaseInLevel3
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the increase (decrease) in the balance of mortgage servicing rights due to reduction in interest rates.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsMortgageServicingRightsIncreaseDecreaseInLevel3DueToReductionInInterestRates
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the Company's investment in certificates issued by the trusts of the newly consolidated VIE's that were classified as Level 3 for fair value measurement purposes.

+ Details

Name:	c_InvestmentInConsolidatedVariableInterestEntitiesCertificatesClassifiedAsLevel3
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of securities which are reclassified as Trading.

+ Details

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

- Definition

Represents the amount of trading losses on derivatives.

+ Details

Name:	c_TradingLossesOnDerivatives
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the net change of assets measured at fair value on a recurring basis using unobservable inputs (Level 3) which have taken place during the period. Such net change may be comprised of changes in fair value (gains or losses) whether realized or unrealized that have been included in earnings, changed net asset value, or other comprehensive income (a separate component of shareholders' equity); purchases, sales, issuances, or settlements of assets; and net transfers in to or out of this category within the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c(1), c(2), c(3)

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

FAIR VALUE MEASUREMENT (Details 3) (USD $)		3 Months Ended			3 Months Ended	6 Months Ended				3 Months Ended			6 Months Ended	3 Months Ended		6 Months Ended	3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended	3 Months Ended			6 Months Ended			3 Months Ended			6 Months Ended
FAIR VALUE MEASUREMENT (Details 3) (USD $)	Mar. 31, 2011 Mortgage-backed securities Trading account assets	Jun. 30, 2011 Mortgage-backed securities Investments:	Mar. 31, 2011 Prime Trading account assets	Mar. 31, 2011 Alt-A Trading account assets	Jun. 30, 2010 Subprime Trading account assets	Jun. 30, 2010 Subprime Trading account assets	Mar. 31, 2011 Subprime Trading account assets	Mar. 31, 2011 Commercial. Trading account assets	Mar. 31, 2011 State and municipal securities Trading account assets	Jun. 30, 2011 Corporate Trading account assets	Mar. 31, 2011 Corporate Trading account assets	Jun. 30, 2010 Corporate Trading account assets	Jun. 30, 2011 Corporate Trading account assets	Jun. 30, 2011 Asset-based financing Trading account assets	Mar. 31, 2011 Asset-based financing Trading account assets	Jun. 30, 2011 Asset-based financing Trading account assets	Jun. 30, 2010 Asset-based financing Investments:	Jun. 30, 2010 Asset-based financing Investments:	Jun. 30, 2010 Other debt securities Trading account assets	Jun. 30, 2011 Non-marketable equity securities Investments:	Mar. 31, 2011 Non-marketable equity securities Investments:	Jun. 30, 2011 Non-marketable equity securities Investments:	Mar. 31, 2011 Auction rate securities Trading account assets	Jun. 30, 2011 Reclassification of debt securities from held-to-maturity to trading account assets Trading account assets	Jun. 30, 2010 Federal funds sold and securities borrowed or purchased under agreements to resell	Mar. 31, 2010 Federal funds sold and securities borrowed or purchased under agreements to resell	Jun. 30, 2011 Federal funds sold and securities borrowed or purchased under agreements to resell	Jun. 30, 2010 Federal funds sold and securities borrowed or purchased under agreements to resell	Jun. 30, 2011 Trading account assets	Jun. 30, 2010 Trading account assets	Jun. 30, 2011 Trading account assets	Jun. 30, 2010 Trading account assets	Mar. 31, 2010 Trading account assets	Mar. 31, 2011 Derivatives	Jun. 30, 2010 Derivatives	Jun. 30, 2011 Derivatives	Jun. 30, 2011 Investments	Mar. 31, 2011 Investments	Jun. 30, 2010 Investments	Jun. 30, 2011 Investments	Jun. 30, 2010 Investments	Jun. 30, 2010 Loans.	Jun. 30, 2010 Mortgage servicing rights	Jun. 30, 2011 Long-term debt.	Jun. 30, 2010 Long-term debt.	Jun. 30, 2011 Long-term debt.	Jun. 30, 2010 Long-term debt.
Fair Value Asset and Liabilities Measured on Recurring Basis Unobservable Input Changes
Increase (decrease) in Level 3 asset balance during period					$ (4,600,000,000)	$ (7,100,000,000)						$ (1,700,000,000)							$ (12,200,000,000)	$ (1,300,000,000)		$ 1,200,000,000		$ 4,300,000,000	$ 4,600,000,000		$ (1,500,000,000)	$ 5,400,000,000	$ (3,900,000,000)	$ (7,400,000,000)	$ (21,400,000,000)	$ (900,000,000)			$ (2,200,000,000)		$ (2,700,000,000)		$ 3,900,000,000	$ (600,000,000)	$ 5,000,000,000	$ 3,500,000,000	$ (1,500,000,000)	$ (1,700,000,000)	$ (2,100,000,000)	$ (1,500,000,000)	$ 1,100,000,000
Net transfers from Level 3 to Level 2		1,000,000,000																									1,400,000,000
Purchases of securities										1,900,000,000	1,800,000,000		3,500,000,000	1,100,000,000	1,300,000,000	2,400,000,000					3,200,000,000	3,300,000,000
Net settlements											(1,500,000,000)				(2,200,000,000)					(800,000,000)		(800,000,000)	(1,100,000,000)			(1,900,000,000)								(1,400,000,000)				(800,000,000)
Increase (decrease) in investments due to paydowns and sales										(1,800,000,000)		(1,500,000,000)	(2,700,000,000)	(1,300,000,000)		(3,300,000,000)				(300,000,000)		(1,100,000,000)
Transfers from Level 2 to Level 3																	6,100,000,000	6,100,000,000							4,200,000,000
Investment in certificates issued by trusts of the newly consolidated VIE's that were classified as Level 3																																	11,100,000,000
Increase (decrease) in level 3 of credit derivatives																																			(3,000,000,000)	(2,100,000,000)
Securities reclassified to Trading	2,800,000,000		1,000,000,000	1,500,000,000			200,000,000	100,000,000	900,000,000		300,000,000				200,000,000
Net trading losses on derivatives																																			1,400,000,000
Increase (decrease) in level 3 of mortgage servicing rights due to reduction in interest rates																																											(1,300,000,000)
Increase (decrease) in level 3 of Long-term debt due to scheduled termination of a structured transaction																																												$ 1,200,000,000		$ 1,200,000,000