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

The maximum percentage of statutory capital that may be paid out as dividends without prior approval from a regulatory agency.

No definition available.

Name:	ago_DividendPaymentRestrictionsSchedulePercentageOfStatutoryCapital
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The maximum percentage of statutory capital and surplus that may be paid out as dividends without prior approval from a regulatory agency.

No definition available.

Name:	ago_DividendPaymentRestrictionsSchedulePercentageOfStatutoryCapitalAndSurplus
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Dividend Payments Restrictions Schedule, Statutory Surplus

No definition available.

Name:	ago_DividendPaymentsRestrictionsScheduleStatutorySurplus
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval, Available in Next Fiscal Quarter

No definition available.

Name:	ago_StatutoryAccountingPracticesStatutoryAmountAvailableforDividendPaymentswithoutRegulatoryApprovalAvailableinNextFiscalQuarter
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Statutory Accounting Practices, Statutory Threshold for Dividend Payments, Percentage of Adjusted Net Investment Income

No definition available.

Name:	ago_StatutoryAccountingPracticesStatutoryThresholdforDividendPaymentsPercentageofAdjustedNetInvestmentIncome
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Statutory Accounting Practices, Statutory Threshold for Dividend Payments, Percentage of Policyholder' Surplus

No definition available.

Name:	ago_StatutoryAccountingPracticesStatutoryThresholdforDividendPaymentsPercentageofPolicyholderSurplus
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Unencumbered Assets which are not held in trust for the benefit of cedants.

No definition available.

Name:	ago_UnencumberedAsset
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_StatutoryAccountingPracticesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of dividends that can be declared or paid without approval of regulatory agency.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Name:	us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=stpr_NY
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dei_LegalEntityAxis=ago_MunicipalAssuranceCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dei_LegalEntityAxis=ago_AssuredGuarantyMunicipalCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=stpr_MD
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dei_LegalEntityAxis=ago_AssuredGuarantyCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=ago_AssuredGuarantyUSHoldingIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=country_BM
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: