Gain Contingency, Credit Derivative Transaction Improperly Calculated Payment, Number

No definition available.

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

- Definition

Represents the amount of payment on the termination of credit derivatives transactions which the defendant owes to complainant as per the calculation of complainant.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of payment on the termination of credit derivatives transactions which the complainant owes to defendant as per the calculation of defendant.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Loss Contingency, Estimated Additional Damages Sought, Value

+ References

No definition available.

+ Details

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

- Definition

Loss Contingency, Number of Claims, Motion to Dismiss Denied

+ References

No definition available.

+ Details

Name:	ago_LossContingencyNumberofClaimsMotiontoDismissDenied
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loss Contingency, Number of Claims, Remaining After Dismissals

+ References

No definition available.

+ Details

Name:	ago_LossContingencyNumberofClaimsRemainingAfterDismissals
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum number of proceedings for recoveries of losses, or failure to obtain recoveries, to have a material impact on the entity's results of operations in a particular quarter or fiscal year.

+ References

No definition available.

+ Details

Name:	ago_MinimumNumberOfProceedingsForRecoveriesToHavePotentialMaterialImpact
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 30

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

+ Details

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

- Definition

Amount of judgment or settlement awarded to (against) the entity in respect of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of claims dismissed.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyClaimsDismissedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyDamagesSoughtValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The total number of new claims filed pertaining to a loss contingency during the period.

+ References

+ Details

Name:	us-gaap_LossContingencyNewClaimsFiledNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfPlaintiffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMaximum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated minimum amount of possible loss from the contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMinimum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=ago_GovernmentalInvestigationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=ago_LehmanBrothersInternationalEuropeVsAgFinancialProductsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_GuaranteeObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=us-gaap_PendingLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationCaseAxis=ago_WellsFargoBankN.A.InterpleaderComplaintMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LitigationCaseAxis=ago_HoustonCasualtyCompanyEuropeVsAssuredGuarantyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LitigationCaseAxis=ago_MDL1950Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_LitigationCaseAxis=ago_NonclassActionCasesConsolidatedwithMDL1950forPretrialProceedingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=ago_ProceedingsRelatedToFormerFinancialProductsBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LitigationCaseAxis=ago_LbhiAndLbsfVsCpt283FsaAndAgmMember
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Data Type:	na
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- Details

Name:	us-gaap_LitigationCaseAxis=ago_LbhiAndLbsfVsCpt207FsaAndAgmMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=us-gaap_SettledLitigationMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	us-gaap_GainContingenciesByNatureAxis=us-gaap_PositiveOutcomeOfLitigationMember
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Data Type:	na
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- Details

Name:	dei_LegalEntityAxis=ago_LehmanBrothersInternationalEuropeMember
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Data Type:	na
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- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
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Commitments and Contingencies - Narrative (Details) € in Millions				1 Months Ended			6 Months Ended	12 Months Ended
	Jan. 30, 2015 USD ($)	May. 28, 2014 EUR (€)	Nov. 19, 2012 USD ($)	May. 31, 2010 Lawsuit	Apr. 30, 2010 Lawsuit	Sep. 30, 2009 Plaintiff	Jun. 30, 2015 Lawsuit	Dec. 31, 2009 Lawsuit	Dec. 31, 2008 Lawsuit	Apr. 10, 2015 USD ($)	Sep. 25, 2013 USD ($)	Nov. 28, 2011 USD ($) Transaction
Commitments and Contingencies Legal Proceedings
Minimum number of proceedings for recoveries to have potential material impact \| Lawsuit							1
Governmental Investigations [Member]
Commitments and Contingencies Legal Proceedings
Number of plaintiffs filing consolidated complaints \| Plaintiff						4
LBIE vs. AG Financial Products [Member] \| AG Financial Products Inc. [Member] \| Guarantee Obligations [Member]
Commitments and Contingencies Legal Proceedings
Number of credit derivative transactions for which termination payment is alleged to be improperly calculated \| Transaction												9
Pending Litigation \| LBIE vs. AG Financial Products [Member] \| AG Financial Products Inc. [Member]
Commitments and Contingencies Legal Proceedings
Termination payments which LBIE owes to AG Financial Products as per calculation of AG Financial Products												$ 29,000,000
Termination payments which AG Financial Products owes to LBIE as per calculation of LBIE												$ 1,400,000,000
Pending Litigation \| Wells Fargo Bank, N.A., Interpleader Complaint [Member] \| AGM [Member]
Commitments and Contingencies Legal Proceedings
Increase in losses as a result of an adverse outcome, minimum											$ 10,000,000
Increase in losses as a result of an adverse outcome, maximum											$ 20,000,000
Pending Litigation \| Houston Casualty Company Europe Vs Assured Guaranty [Member] \| Radian [Member]
Commitments and Contingencies Legal Proceedings
Damages sought \| €		€ 15.0
Estimated additional damage sought \| €		€ 3.1
Pending Litigation \| MDL 1950 [Member]
Commitments and Contingencies Legal Proceedings
Number of putative class action lawsuits filed in federal court \| Lawsuit									9
Pending Litigation \| MDL 1950 [Member] \| AGMH [Member]
Commitments and Contingencies Legal Proceedings
Number of putative class action lawsuits filed in federal court \| Lawsuit									4
Pending Litigation \| MDL 1950 [Member] \| AGM and AGMH [Member]
Commitments and Contingencies Legal Proceedings
Number of putative class action lawsuits filed in federal court \| Lawsuit									5
Pending Litigation \| Non-class Action Cases Consolidated with MDL 1950 for Pretrial Proceedings [Member] \| AGM and AGMH [Member] \| Proceedings Related to Former Financial Products Business [Member]
Commitments and Contingencies Legal Proceedings
Number of putative class action lawsuits filed in federal court \| Lawsuit									5
Pending Litigation \| Non-class Action Cases Consolidated with MDL 1950 for Pretrial Proceedings [Member] \| AGM and AGUS [Member] \| Proceedings Related to Former Financial Products Business [Member]
Commitments and Contingencies Legal Proceedings
Number of putative class action lawsuits filed in federal court \| Lawsuit				5				6
Number of cases voluntarily dismissed with prejudice \| Lawsuit							1
Number of claims remaining after dismissals \| Lawsuit							5
Number of non-class action lawsuits for which dismissal was denied \| Lawsuit					10
Pending Litigation \| LBHI and LBSF vs CPT 283, FSA and AGM [Member] \| AGM [Member]
Commitments and Contingencies Legal Proceedings
Termination payments which LBIE owes to AG Financial Products as per calculation of AG Financial Products			$ 43,800,000
Damages sought			67,300,000
Pending Litigation \| LBHI and LBSF vs CPT 207, FSA and AGM [Member] \| AGM [Member]
Commitments and Contingencies Legal Proceedings
Termination payments which LBIE owes to AG Financial Products as per calculation of AG Financial Products			492,555
Damages sought			$ 1,500,000
Settled Litigation [Member] \| LBHI and LBSF vs CPT 207, FSA and AGM [Member] \| AGM [Member]
Commitments and Contingencies Legal Proceedings
Litigation Settlement, Amount	$ 20,000,000
Positive Outcome of Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Gain contingency, number of credit derivative transactions with improperly calculated payments \| Transaction												28
Minimum [Member] \| Positive Outcome of Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Gain contingency, unrecorded amount										$ 200,000,000
Maximum [Member] \| Positive Outcome of Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Gain contingency, unrecorded amount										$ 500,000,000