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

Financial Guarantee Insurance Contracts, Premiums Earned, Net

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsPremiumsEarnedNet
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the amount of premium revenue on financial guaranty insurance contracts recognized during the period, excluding acceleration of premium earnings and accretion of discount on net premium receivable.

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsScheduledNetEarnedPremiums
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Premiums Earned, Net, Specialty Insurance and Reinsurance

No definition available.

Name:	ago_PremiumsEarnedNetSpecialtyInsuranceandReinsurance
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

This element represents the amount of premium revenue on financial guarantee insurance contracts recognized during the period that was accelerated for revenue recognition purposes.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 944
-SubTopic 605
-Section 50
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Name:	us-gaap_FinancialGuaranteeInsuranceContractsAcceleratedPremiumRevenueAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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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_GuaranteeObligationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 942
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-Section S99
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-Subparagraph (SX 210.9-04(13)(c))
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 605
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