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
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 4
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-Publisher FASB
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Name:	us-gaap_FinancialGuaranteeInsuranceContractsAcceleratedPremiumRevenueAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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- References

No definition available.

Name:	us-gaap_InsuranceAbstract
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
-Topic 944
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(1))
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