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 convicted of conspiracy and fraud who had worked at Financial Guaranty Insurance Company.

No definition available.

Name:	ago_NumberOfPersonsConvictedOfConspiracyAndFraudWhoWorkedAtFinancialGuarantyInsuranceCompany
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

Payment on Termination of Credit Derivative Transaction Owed by Complainant as Per Defendants Calculation1

No definition available.

Name:	ago_PaymentOnTerminationOfCreditDerivativeTransactionOwedByComplainantAsPerDefendantsCalculation1
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Payment on Termination of Credit Derivative Transaction Owed by Complainant as Per Defendants Calculation2

No definition available.

Name:	ago_PaymentOnTerminationOfCreditDerivativeTransactionOwedByComplainantAsPerDefendantsCalculation2
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

Payment on Termination of Credit Derivative Transaction Owed to Complainant as Per Complainants Calculation1

No definition available.

Name:	ago_PaymentOnTerminationOfCreditDerivativeTransactionOwedToComplainantAsPerComplainantsCalculation1
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Payment on Termination of Credit Derivative Transaction Owed to Complainant as Per Complainants Calculation2

No definition available.

Name:	ago_PaymentOnTerminationOfCreditDerivativeTransactionOwedToComplainantAsPerComplainantsCalculation2
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

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

No definition available.