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

No definition available.

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

Represents the entity's estimate of the present value of future claim payments, net of reinsurance and net of salvage and subrogation which includes the present value benefit of estimated recoveries for breaches of R&W, including the effect of consolidating VIEs.

No definition available.

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

No definition available.

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

Represents the estimate of the present value of future claim payments related to consolidating of financial guaranty VIEs, net of reinsurance and net of salvage and subrogation which includes the present value benefit of estimated recoveries for breaches of R&W.

No definition available.

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

Represents the reserve for losses and loss adjustment expenses, net of reinsurance recoverable on unpaid losses and net of salvage and subrogation recoverable.

No definition available.

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

Represents the effect on reserve for losses and loss adjustment expenses, net of reinsurance recoverable on unpaid losses and net of salvage and subrogation recoverable related to consolidating VIEs.

No definition available.

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

Represents the reserve for losses and loss adjustment expenses, net of reinsurance recoverable on unpaid losses, net of salvage and subrogation recoverable, for contracts ceded by the entity.

No definition available.

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

Represents the reserve for losses and loss adjustment expenses, net of reinsurance recoverable on unpaid losses, net of salvage and subrogation recoverable, for contracts the entity has issued directly or assumed.

No definition available.

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

ago_ReserveForLossesAndLossAdjustmentExpenseswithcreditdeteriorationNetOfReinsuranceAndSalvageAndSubrogationRecoveriesBeforeVieAdjustment

No definition available.

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

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationExpectedCashFlowsAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the gross claim liability for financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts related to consolidating VIEs.

No definition available.

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

No definition available.

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

No definition available.

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

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration Gross Claim Liability Potential Recoveries, Other, Ceded

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration Gross Claim Liability Potential Recoveries, Other, Gross

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Gross Claim Liability Potential Recoveries, Undiscounted Representations and Warranties, Ceded

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Gross Claim Liability Potential Recoveries, Undiscounted Representations and Warranties, Gross

No definition available.

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

This element represents the gross subtotal of gross potential recoveries and gross claim liability for financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts the entity has issued.

No definition available.

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

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilitySubtotalAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

No definition available.

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

No definition available.

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

No definition available.

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

No definition available.

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

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsInterestAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the amount of insured contractual payments outstanding on the underlying insured obligations for financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts ceded by the entity.

No definition available.

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

No definition available.

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

This element represents the amount of insured contractual payments outstanding attributable to interest accrued on the underlying insured obligations for financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts ceded by the entity.

No definition available.

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

No definition available.

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

No definition available.

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

No definition available.

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

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the amount of insured contractual payments outstanding attributable to the principal of the underlying insured obligations for financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts ceded by the entity.

No definition available.

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

No definition available.

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

No definition available.

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

Represents the number of issued and outstanding contracts for each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts ceded by the entity.

No definition available.

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
Namespace Prefix:	ago_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

No definition available.

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingGross
Namespace Prefix:	ago_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

No definition available.

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingNet
Namespace Prefix:	ago_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfRisksAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveriesAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the gross potential recoveries against the gross claim liability for financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts related to consolidating VIEs.

No definition available.

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

No definition available.

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

No definition available.

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

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Gross Potential Recoveries, Other

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Gross Potential Recoveries, Other, before VIE Adjustment

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Gross Potential Recoveries, Undiscounted R and W

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Gross Potential Recoveries Undiscounted R and W before VIE Adjustment

No definition available.

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

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscountAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the net discount consisting of the difference between the discount related to the claim liability for and potential recoveries thereof related to financial guaranty insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts related to consolidating VIEs.

No definition available.

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

No definition available.

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

No definition available.

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

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Other, Gross Potential Recoveries Adjustment for Consolidating VIEs

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Undiscounted R and W, Gross Potential Recoveries Adjustment for Consolidating VIEs

No definition available.

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

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationRemainingWeightedAverageContractPeriodAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the remaining weighted average contract period of financial guaranty insurance contracts for each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts ceded by the entity.

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationRemainingWeightedAverageContractPeriodCeded
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationRemainingWeightedAverageContractPeriodGross
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationRemainingWeightedAverageContractPeriodNet
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReservesSalvageAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenueAbstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the amount of unearned premium revenue, reported on or included in the statement of financial position, related to financial guarantee insurance contracts and presented in the schedule of insured financial obligations with credit deterioration in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts ceded by the entity.

No definition available.

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

This element represents the amount of unearned premium revenue, reported on or included in the statement of financial position, related to financial guaranty insurance contracts and presented in the schedule of insured financial obligations with credit deterioration in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guaranty insurance contracts the entity has issued directly or assumed.

No definition available.

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

No definition available.

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

No definition available.

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

Remaining weighted average contract period of financial guarantee insurance contracts, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 9

-Subparagraph (a)(5)(ii)

-URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 55

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=6933462&loc=SL5751133-161288

Name:	us-gaap_InsuredFinancialObligationsWithCreditDeteriorationRemainingWeightedAverageContractPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

This element represents the gross claim liability for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 55

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=6933462&loc=SL5751133-161288

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 9

-Subparagraph (a)(5)(iv)

-URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292

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

This element represents the amount of insured contractual payments outstanding on the underlying insured obligations for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 55

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=6933462&loc=SL5751133-161288

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 9

-Subparagraph (a)(5)(iii)

-URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292

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

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

This element represents the amount of insured contractual payments outstanding attributable to interest accrued on the underlying insured obligations for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 55

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=6933462&loc=SL5751133-161288

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 9

-Subparagraph (a)(5)(iii)

-URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292

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

This element represents the amount of insured contractual payments outstanding attributable to the principal of the underlying insured obligations for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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-Publisher FASB

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This element represents the number of issued and outstanding contracts for each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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This element represents the gross potential recoveries against the gross claim liability for financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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This element represents the net discount consisting of the difference between the discount related to the claim liability for and potential recoveries thereof related to financial guarantee insurance contracts presented in the context of each surveillance grouping or category used by management to monitor and track potential deterioration in the credit worthiness of the insured party's ability to meet its financial obligations related to the contracts underlying financial guarantee insurance contracts the entity has issued.

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