Name:	ago_GainContingencyAllegationsPaymentForTerminationofCreditDerivativeTransactionsOwedbyDefendanttoPlaintiffAsPerCalculationofPlaintiff
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 plaintiff owes to defendant as per the calculation of defendant.

No definition available.

Name:	ago_GainContingencyAllegationsPaymentForTerminationofCreditDerivativeTransactionsOwedbyPlaintifftoDefendantAsPerCalculationofDefendant
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
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Gain Contingency, Allegations, Payment For Termination of Other Credit Derivative Transactions Owed by Plaintiff to Defendant As Per Calculation of Defendant

No definition available.

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

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

No definition available.

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

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

No definition available.

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

The amount or range of possible amounts of gain that could be realized upon the resolution of a contingency.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 30
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_LossContingenciesLineItems
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Data Type:	xbrli:stringItemType
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Namespace Prefix:
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