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Balance Type:	debit
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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
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Data Type:	num:percentItemType
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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
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Data Type:	num:percentItemType
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Dividend Payments Restrictions Schedule, Statutory Surplus

No definition available.

Name:	ago_DividendPaymentsRestrictionsScheduleStatutorySurplus
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Holding Company's Percent Ownership of Common Stock

No definition available.

Name:	ago_HoldingCompanysPercentOwnershipofCommonStock
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the discount rate used to calculate present value for surveillance purposes.

No definition available.

Name:	ago_InsuredFinancialObligationsDiscountRate
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Statutory Accounting Practices, Contingency Reserves Reassumed

No definition available.

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

Statutory Accounting Practices, Contingency Reserves, Release of Assets

No definition available.

Name:	ago_StatutoryAccountingPracticesContingencyReservesReleaseofAssets
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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Statutory Accounting Practices, Deferred Tax Assets, Adjusted Surplus Threshold, Percentage

No definition available.

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

Statutory Accounting Practices, Deferred Tax Assets, Adjusted Surplus Threshold, Realization Period

No definition available.

Name:	ago_StatutoryAccountingPracticesDeferredTaxAssetsAdjustedSurplusThresholdRealizationPeriod
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Balance Type:	na
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Statutory Accounting Practices, Intercompany Transaction, Consideration Transferred

No definition available.

Name:	ago_StatutoryAccountingPracticesIntercompanyTransactionConsiderationTransferred
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Balance Type:	credit
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Statutory Accounting Practices, Intercompany Transaction, Proceeds From Distribution By Subsidiary

No definition available.

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Data Type:	xbrli:monetaryItemType
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Statutory Accounting Practices, Intercompany Transaction, Repayment of Surplus Notes

No definition available.

Name:	ago_StatutoryAccountingPracticesIntercompanyTransactionRepaymentofSurplusNotes
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Statutory Accounting Practices, Reserves for Contingencies Reassumed

No definition available.

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Balance Type:	debit
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Statutory Accounting Practices, Reserves for Contingencies Reassumed, Incremental Reassumption, Period

No definition available.

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Data Type:	xbrli:durationItemType
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Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval, Available in Next Fiscal Quarter

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Statutory Accounting Practices, Statutory Threshold for Dividend Payments, Percentage of Adjusted Net Investment Income

No definition available.

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Data Type:	num:percentItemType
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Statutory Accounting Practices, Statutory Threshold for Dividend Payments, Percentage of Policyholder' Surplus

No definition available.

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Data Type:	num:percentItemType
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Unencumbered Assets which are not held in trust for the benefit of cedants.

No definition available.

Name:	ago_UnencumberedAsset
Namespace Prefix:	ago_
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Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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The amount of total capital as defined in the regulations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 1H
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Period Type:	instant

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

No definition available.

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Data Type:	num:percentItemType
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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

No definition available.

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Data Type:	num:percentItemType
Balance Type:	na
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.

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

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

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The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of stock repurchase plan authorized.

No definition available.

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

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Balance Type:
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Name:	dei_LegalEntityAxis=ago_AssuredGuarantyCorpMember
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Data Type:	na
Balance Type:
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Name:	dei_LegalEntityAxis=ago_MunicipalAssuranceCorpMember
Namespace Prefix:
Data Type:	na
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Name:	dei_LegalEntityAxis=ago_AssuredGuarantyMunicipalCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
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Name:	dei_LegalEntityAxis=ago_MunicipalAssuranceCorpHoldingsMember
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Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=ago_AssuredGuarantyMunicipalCorpMember
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Name:	us-gaap_CounterpartyNameAxis=ago_MunicipalAssuranceCorpMember
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Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=ago_AssuredGuarantyCorpMember
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Data Type:	na
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Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=ago_MunicipalAssuranceCorpHoldingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=stpr_NY
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	dei_LegalEntityAxis=ago_AssuredGuarantyMunicipalCorpAndMunicipalAssuranceCorpMember
Namespace Prefix:
Data Type:	na
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Data Type:	na
Balance Type:
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Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=ago_AssuredGuarantyUSHoldingIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=country_BM
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
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