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

-- None. No documentation exists for this element. --

No definition available.

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

Schedule Of Insured Financial Obligations With Credit Deterioration Gross Claim Liability, Ceded

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

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_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

-- None. No documentation exists for this element. --

No definition available.

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_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

-- None. No documentation exists for this element. --

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

-- None. No documentation exists for this element. --

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Claim Liability Ceded

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Net Claim Liability, Ceded

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Net Claim Liability, Net of Reinsurance Recoverable

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Net Claim Liability, Undiscounted, Direct Assumed

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Net Claim Liability, Undiscounted, Direct Assumed, Net

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
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, Ceded, Net Discount

No definition available.

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

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

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
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, Net of Reinsurance Recoverable, Discount

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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_ScheduleofInsuredFinancialObligationswithCreditDeteriorationRemainingWeightedAverageContractPeriodNet
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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Claim Liability, Ceded

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Unearned Premium Revenue, Ceded

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
Namespace Prefix:	ago_
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Schedule of Insured Financial Obligations with Credit Deterioration, Statement of Financial Position, Unearned Premium Revenue, Net of Reinsurance Recoverable

No definition available.

Name:	ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
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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)
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Data Type:	xbrli:durationItemType
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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.

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Name:	us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
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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.

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- References

No definition available.

Name:	us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingAbstract
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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.

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Name:	us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
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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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This element represents the net claim liability 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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- References

No definition available.

Name:	us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiabilityAbstract
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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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Name:	us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
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Data Type:	xbrli:decimalItemType
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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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This element represents the claim liability, 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 guarantee insurance contracts the entity has issued.

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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 guarantee insurance contracts the entity has issued.

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