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

- Details

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

Amount of increase (decrease) in loss contingency liability.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualCarryingValuePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

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

No definition available.