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 corporate trading debt securities classified as Level 3 assets, due to paydowns and sales.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsCorporateTradingSecuritiesDueToPaydownsAndSalesIncreaseDecreaseInLevel3
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

Represents the increase (decrease) in the balance of investments, due to the purchase of investments in private equity and hedge funds.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsInvestmentsIncreaseDecreaseInLevel3DueToPurchaseOfPrivateEquityAndHedgeFunds
Namespace Prefix:	c
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the increase (decrease) in the balance of investments, due to sales and redemptions of investments in private equity and hedge funds.

+ Details

Name:	c_FairValueMeasurementWithUnobservableInputsInvestmentsIncreaseDecreaseInLevel3DueToSalesAndRedemptionsOfPrivateEquityAndHedgeFund
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 to scheduled 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

Represents total gains or losses during the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3) due to credit spreads widening, which are included in earnings or resulted in a change in the net asset value and are included in the income statement in principal transactions.

+ Details

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

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value, and are included in the income statement in principal transactions.

+ Details

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

- Definition

Represents total gains or losses during the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3), recorded on total return swaps referencing returns on corporate loans which are included in earnings or resulted in a change in the net asset value.

+ Details

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

- Definition

Issues 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_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues
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				3 Months Ended	6 Months Ended	9 Months Ended		3 Months Ended			3 Months Ended		6 Months Ended	9 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended			6 Months Ended		9 Months Ended		3 Months Ended			6 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	3 Months Ended			6 Months Ended		9 Months Ended		3 Months Ended	6 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended			6 Months Ended		9 Months Ended
FAIR VALUE MEASUREMENT (Details 3) (USD $)	Sep. 30, 2011	Sep. 30, 2010 Mortgage-backed securities Trading account assets	Sep. 30, 2011 Mortgage-backed securities Trading account assets	Sep. 30, 2011 Mortgage-backed securities Investments:	Sep. 30, 2010 Mortgage-backed securities Investments:	Sep. 30, 2011 Prime Trading account assets	Sep. 30, 2011 Alt-A Trading account assets	Jun. 30, 2010 Subprime Trading account assets	Jun. 30, 2010 Subprime Trading account assets	Sep. 30, 2010 Subprime Trading account assets	Sep. 30, 2011 Subprime Trading account assets	Sep. 30, 2010 Non-U.S. residential Trading account assets	Sep. 30, 2011 Commercial. Trading account assets	Sep. 30, 2011 State and municipal securities Trading account assets	Sep. 30, 2011 Corporate Trading account assets	Jun. 30, 2010 Corporate Trading account assets	Jun. 30, 2011 Corporate Trading account assets	Sep. 30, 2011 Corporate Trading account assets	Sep. 30, 2010 Corporate Trading account assets	Sep. 30, 2011 Asset-based financing Trading account assets	Sep. 30, 2010 Asset-based financing Trading account assets	Jun. 30, 2011 Asset-based financing Trading account assets	Sep. 30, 2011 Asset-based financing Trading account assets	Sep. 30, 2010 Asset-based financing Trading account assets	Sep. 30, 2010 Asset-based financing Investments:	Jun. 30, 2010 Asset-based financing Investments:	Jun. 30, 2010 Asset-based financing Investments:	Sep. 30, 2010 Asset-based financing Investments:	Jun. 30, 2010 Other debt securities Trading account assets	Sep. 30, 2010 Other debt securities Trading account assets	Sep. 30, 2011 Non-marketable equity securities Investments:	Sep. 30, 2010 Non-marketable equity securities Investments:	Jun. 30, 2011 Non-marketable equity securities Investments:	Sep. 30, 2011 Non-marketable equity securities Investments:	Jun. 30, 2011 Reclassification of debt securities from held-to-maturity to trading account assets Trading account assets	Sep. 30, 2011 Reclassification of debt securities from held-to-maturity to trading account assets Trading account assets	Sep. 30, 2011 Federal funds sold and securities borrowed or purchased under agreements to resell	Sep. 30, 2010 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 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	Sep. 30, 2011 Federal funds sold and securities borrowed or purchased under agreements to resell	Sep. 30, 2010 Federal funds sold and securities borrowed or purchased under agreements to resell	Sep. 30, 2011 Trading account assets	Sep. 30, 2010 Trading account assets	Jun. 30, 2010 Trading account assets	Jun. 30, 2011 Trading account assets	Jun. 30, 2010 Trading account assets	Sep. 30, 2010 Trading account assets	Mar. 31, 2010 Trading account assets	Dec. 31, 2009 Trading account assets	Sep. 30, 2011 Credit derivatives Derivatives	Sep. 30, 2011 Credit derivatives Derivatives	Sep. 30, 2010 Derivatives	Jun. 30, 2010 Derivatives	Jun. 30, 2011 Derivatives	Sep. 30, 2011 Investments:	Sep. 30, 2010 Investments:	Jun. 30, 2010 Investments:	Jun. 30, 2011 Investments:	Jun. 30, 2010 Investments:	Sep. 30, 2011 Investments:	Sep. 30, 2010 Investments:	Sep. 30, 2011 Loans.	Jun. 30, 2010 Loans.	Sep. 30, 2011 Loans.	Sep. 30, 2010 Loans.	Sep. 30, 2011 Mortgage servicing rights	Jun. 30, 2010 Mortgage servicing rights	Sep. 30, 2011 Mortgage servicing rights	Sep. 30, 2010 Mortgage servicing rights	Sep. 30, 2011 Long-term debt.	Jun. 30, 2011 Long-term debt.	Jun. 30, 2010 Long-term debt.	Jun. 30, 2011 Long-term debt.	Jun. 30, 2010 Long-term debt.	Sep. 30, 2011 Long-term debt.
Fair Value Asset and Liabilities Measured on Recurring Basis Unobservable Input Changes
Increase (decrease) in Level 3 asset balance during period		$ (800,000,000)						$ (4,600,000,000)	$ (7,100,000,000)	$ (7,600,000,000)						$ (1,700,000,000)					$ 3,300,000,000			$ 4,500,000,000					$ (12,200,000,000)	$ (12,100,000,000)	$ (400,000,000)		$ 1,200,000,000	$ 800,000,000	$ 4,300,000,000	$ 4,300,000,000	$ 1,300,000,000		$ 4,600,000,000	$ (1,500,000,000)	$ 5,400,000,000	$ (1,500,000,000)	$ 7,000,000,000	$ (800,000,000)	$ 3,400,000,000	$ (7,400,000,000)	$ (900,000,000)	$ (21,400,000,000)	$ (18,000,000,000)			$ 1,800,000,000	$ (300,000,000)	$ (1,100,000,000)	$ (2,200,000,000)		$ (1,300,000,000)	$ (7,800,000,000)	$ 3,900,000,000	$ (600,000,000)	$ 5,000,000,000	$ 1,900,000,000	$ (2,800,000,000)	$ 1,100,000,000	$ 3,500,000,000	$ 1,400,000,000	$ 3,700,000,000	$ (1,400,000,000)	$ (1,500,000,000)	$ (1,700,000,000)	$ (2,500,000,000)	$ (1,700,000,000)		$ (2,100,000,000)	$ (1,500,000,000)	$ 1,100,000,000	$ (2,100,000,000)
Net transfers from Level 3 to Level 2				1,000,000,000	(1,500,000,000)																				(4,900,000,000)			(4,900,000,000)									1,100,000,000			1,400,000,000		1,400,000,000																(6,900,000,000)					(600,000,000)
Purchases of securities															1,800,000,000		3,500,000,000			600,000,000		2,400,000,000											3,300,000,000	4,200,000,000
Net realized/unrealized gains (losses) included in principal transactions, assets																																																				1,700,000,000	1,100,000,000
Net settlements												2,400,000,000									1,500,000,000										(800,000,000)	600,000,000	(800,000,000)																				1,400,000,000	800,000,000			(800,000,000)	1,400,000,000				1,200,000,000															2,000,000,000
Gains on bespoke CDO and index CDO positions due to credit spreads widening																																																				700,000,000	700,000,000
Gains recorded on total return swaps referencing returns on corporate loans																																																				600,000,000	600,000,000
Increase (decrease) in investments due to sales and redemptions of investments in private equity and hedge funds																															(1,100,000,000)
Increase (decrease) in investments due to purchase of investments in private equity and hedge funds																															800,000,000
Increase (decrease) in investments due to paydowns and sales															(1,800,000,000)	(1,500,000,000)	(2,700,000,000)	(2,900,000,000)		(1,000,000,000)		(3,300,000,000)	(5,000,000,000)								(300,000,000)		(1,100,000,000)											(3,300,000,000)																		1,700,000,000	2,100,000,000
Transfers from Level 2 to Level 3		1,400,000,000		1,000,000,000																	4,900,000,000			4,900,000,000		6,100,000,000	6,100,000,000	4,800,000,000										1,700,000,000	4,200,000,000				5,900,000,000											300,000,000										600,000,000		400,000,000
Issuance, assets																																																																800,000,000		1,900,000,000
Investment in certificates issued by trusts of the newly consolidated VIE's that were classified as Level 3																																																		11,100,000,000	11,100,000,000
Increase (decrease) in level 3 of credit derivatives	1,800,000,000																																																						(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			300,000,000		200,000,000	1,000,000,000		200,000,000	1,000,000,000																				4,300,000,000
Net trading losses on derivatives																																																						600,000,000	1,400,000,000
Increase (decrease) in level 3 of mortgage servicing rights due to reduction in interest rates																																																																				(1,400,000,000)	(1,300,000,000)	(1,700,000,000)	2,000,000,000
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
Increase (decrease) in level 3 of corporate trading debt securities due to paydowns and sales																			$ (2,200,000,000)