Name:	ago_InsuredFinancialObligationsPrincipalAmountSubjectToPutativeClassAction
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the minimum number of proceedings for recoveries of losses, or failure to obtain recoveries, to have a material impact on the entity's results of operations in a particular quarter or fiscal year.

No definition available.

Name:	ago_MinimumNumberOfProceedingsForRecoveriesToHavePotentialMaterialImpact
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of non-class action lawsuits for which the entity requested dismissal and the dismissal was denied by the court.

No definition available.

Name:	ago_NonClassActionLawsuitsNumberDismissalDenied
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents number of commutations disputed.

No definition available.

Name:	ago_NumberOfCommutations
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of credit derivative transactions which the entity has improperly terminated as per the allegations of the complainants.

No definition available.

Name:	ago_NumberOfCreditDerivativeTransactionsAllegedToBeImproperlyTerminated
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the number of credit derivative transactions for which the entity has improperly calculated the termination payment as per the allegations of the complainants.

No definition available.

Name:	ago_NumberOfCreditDerivativeTransactionsForWhichTerminationPaymentAllegedToBeImproperlyCalculated
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the number of non-class action lawsuits filed naming the entity among other defendants.

No definition available.

Name:	ago_NumberOfNonClassActionLawsuits
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of persons indicted who had worked at Financial Guaranty Insurance Company.

No definition available.

Name:	ago_NumberOfPersonsIndictedWhoWorkedAtFinancialGuarantyInsuranceCompany
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the number of putative class action lawsuits that were filed in a federal court alleging federal antitrust violations in the municipal derivatives industry.

No definition available.

Name:	ago_NumberOfPutativeClassActionLawsuitsFiled
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the amount of payment on the termination of credit derivatives transactions which the complainant owes to defendant as per the calculation of defendant.

No definition available.

Name:	ago_PaymentOnTerminationOfCreditDerivativeTransactionOwedByComplainantAsPerDefendantsCalculation
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the amount of payment on the termination of credit derivatives transactions which the defendant owes to complainant as per the calculation of complainant.

No definition available.

Name:	ago_PaymentOnTerminationOfCreditDerivativeTransactionOwedToComplainantAsPerComplainantsCalculation
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the percentage of amount in segregated account payable in cash.

No definition available.

Name:	ago_PercentageOfSegregatedAccountPayableInCash
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the percentage of amount in segregated account payable in surplus notes issued.

No definition available.

Name:	ago_PercentageOfSegregatedAccountPayableInNotesIssued
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

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-Paragraph 10

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

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

Number of plaintiffs that have filed claims pertaining to a loss contingency.

No definition available.