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Financial Guaranty Insurance Losses - BIG Transaction Loss Summary (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
risk
Dec. 31, 2013
risk
Discount    
Total $ (413)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount  
Reserves (salvage)    
Total 567ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries 386ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
BIG [Member]    
Number of risks    
Total (in contracts) 358us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[1] 384us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[1]
Remaining weighted average contract period    
Total (in years) 10 years 3 months 18 days 10 years 6 months
Principal    
Total 15,222ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
17,745ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Interest    
Total 7,651ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
9,290ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Total net outstanding exposure    
Total 22,873ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[2] 27,035ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[2]
Expected cash outflows (inflows)    
Total 3,118us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
3,252us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Potential recoveries    
Total, Undiscounted R&W (239)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesofRepresentationsandWarrantiesNetUndiscounted
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
(568)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesofRepresentationsandWarrantiesNetUndiscounted
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Total, Other (1,477)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesNetOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
(1,537)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesNetOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[3]
Total (1,716)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[3] (2,105)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Subtotal    
Total 1,402ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
1,147ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Discount    
Total (413)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
(406)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Present value of expected cash flows    
Net expected loss to be paid 989ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
741ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Deferred premium revenue    
Total 584ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
681ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
Reserves (salvage)    
Total 571ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[4] 389ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
[4]
BIG [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member]    
Number of risks    
Total (in contracts) 358us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[1] 384us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[1]
Remaining weighted average contract period    
Total (in years) 10 years 3 months 18 days 10 years 6 months
Principal    
Total 15,222ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
17,745ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Interest    
Total 7,651ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
9,290ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Total net outstanding exposure    
Total 22,873ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[2] 27,035ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[2]
Expected cash outflows (inflows)    
Total 3,463us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
3,942us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Potential recoveries    
Total, Undiscounted R&W (247)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesofRepresentationsandWarrantiesNetUndiscounted
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
(640)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesofRepresentationsandWarrantiesNetUndiscounted
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Total, Other (1,654)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesNetOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
(2,044)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesNetOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[3]
Total (1,901)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[3] (2,684)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Subtotal    
Total 1,562ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
1,258ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Discount    
Total (447)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
(457)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Present value of expected cash flows    
Net expected loss to be paid 1,115ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
801ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Deferred premium revenue    
Total 700ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
859ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
Reserves (salvage)    
Total 650ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[4] 407ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
[4]
BIG [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | BIG 1 [Member]    
Number of risks    
Ceded (in contracts) (59)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[1] (72)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[1]
Total (in contracts) 164us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[1] 185us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[1]
Remaining weighted average contract period    
Gross (in years) 9 years 10 months 24 days 10 years 6 months
Ceded (in years) 7 years 4 months 24 days 8 years 1 month
Principal    
Gross 12,358us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipal
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
15,132us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipal
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded (2,163)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(2,741)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Interest    
Gross 6,350us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
8,114us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded (838)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(1,144)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Total net outstanding exposure    
Gross 18,708us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[2] 23,246us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[2]
Ceded (3,001)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[2] (3,885)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[2]
Expected cash outflows (inflows)    
Gross 1,762us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
1,853us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded (626)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(528)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Total 39us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(13)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Potential recoveries    
Gross, Undiscounted R&W (39)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesGross
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(105)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesGross
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded, Undiscounted R&W 0ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
1ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Gross, Other (1,687)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(1,774)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[3]
Ceded, Other 608ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesCededOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
513ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesCededOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[3]
Ceded 608ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
514ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Gross (1,726)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(1,879)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Subtotal    
Gross 36ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumed
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(26)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumed
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded (18)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(14)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Discount    
Gross 3us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
13us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded 0ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityCededNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
0ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityCededNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Present value of expected cash flows    
Ceded (18)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(14)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Deferred premium revenue    
Gross 378us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenue
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
517us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenue
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Ceded (70)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
(90)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
Reserves (salvage)    
Gross (42)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[4] (114)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[4]
Ceded (5)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[4] 1ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel1Member
[4]
BIG [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | BIG 2 [Member]    
Number of risks    
Ceded (in contracts) (15)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[1] (24)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[1]
Total (in contracts) 75us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[1] 80us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[1]
Remaining weighted average contract period    
Gross (in years) 10 years 1 month 6 days 8 years 3 months
Ceded (in years) 8 years 10 months 24 days 5 years 11 months
Principal    
Gross 2,421us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipal
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
2,483us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipal
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded (286)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(160)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Interest    
Gross 1,274us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
1,181us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded (121)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(53)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Total net outstanding exposure    
Gross 3,695us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[2] 3,664us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[2]
Ceded (407)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[2] (213)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[2]
Expected cash outflows (inflows)    
Gross 763us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
1,038us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded (77)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(40)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Total 392us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
241us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Potential recoveries    
Gross, Undiscounted R&W (48)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesGross
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(201)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesGross
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded, Undiscounted R&W 2ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
8ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Gross, Other (206)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(470)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[3]
Ceded, Other 5ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesCededOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
19ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesCededOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[3]
Ceded 7ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
27ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Gross (254)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(671)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Subtotal    
Gross 509ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumed
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
367ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumed
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded (70)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(13)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Discount    
Gross (117)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(126)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded 11ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityCededNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
3ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityCededNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Present value of expected cash flows    
Ceded (59)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(10)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Deferred premium revenue    
Gross 119us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenue
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
163us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenue
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Ceded (6)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
(7)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
Reserves (salvage)    
Gross 278us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[4] 117us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[4]
Ceded (53)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[4] (4)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel2Member
[4]
BIG [Member] | Consolidated Entity Excluding Consolidation of Variable Interest Entities (VIE) [Member] | BIG 3 [Member]    
Number of risks    
Ceded (in contracts) (38)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[1] (34)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[1]
Total (in contracts) 119us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[1] 119us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNumberOfContractsIssuedAndOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[1]
Remaining weighted average contract period    
Gross (in years) 9 years 7 months 6 days 9 years 9 months
Ceded (in years) 6 years 10 months 24 days 7 years 2 months
Principal    
Gross 3,067us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipal
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
3,189us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipal
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded (175)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(158)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingPrincipalCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Interest    
Gross 1,034us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
1,244us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterest
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded (48)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(52)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingInterestCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Total net outstanding exposure    
Gross 4,101us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[2] 4,433us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstanding
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[2]
Ceded (223)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[2] (210)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationInsuredContractualPaymentsOutstandingCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[2]
Expected cash outflows (inflows)    
Gross 1,716us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
1,681us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded (75)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(62)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Total 788us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
622us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Potential recoveries    
Gross, Undiscounted R&W (171)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesGross
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(356)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesGross
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded, Undiscounted R&W 9ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
13ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesUndiscountedRepresentationsandWarrantiesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Gross, Other (404)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(351)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[3]
Ceded, Other 30ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesCededOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
19ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationGrossClaimLiabilityPotentialRecoveriesCededOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[3]
Ceded 39ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
32ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Gross (575)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(707)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityGrossPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Subtotal    
Gross 1,141ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumed
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
974ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumed
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded (36)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(30)ago_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationGrossClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Discount    
Gross (353)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(352)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilityNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded 9ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityCededNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
5ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityCededNetDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Present value of expected cash flows    
Ceded (27)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(25)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Deferred premium revenue    
Gross 312us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenue
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
303us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionUnearnedPremiumRevenue
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Ceded (33)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
(27)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
Reserves (salvage)    
Gross 482us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[4] 420us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationStatementOfFinancialPositionClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[4]
Ceded (10)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[4] (13)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionClaimLiabilityCeded
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_ConsolidatedEntityExcludingVariableInterestEntitiesVIEMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_InternalNoninvestmentGradeLevel3Member
[4]
BIG [Member] | Variable Interest Entity, Primary Beneficiary [Member]    
Expected cash outflows (inflows)    
Total (345)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
(690)us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationNetClaimLiability
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Potential recoveries    
Total, Undiscounted R&W 8ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesofRepresentationsandWarrantiesNetUndiscounted
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
72ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesofRepresentationsandWarrantiesNetUndiscounted
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Total, Other 177ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesNetOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
507ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityPotentialRecoveriesNetOther
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
[3]
Total 185ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
579ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetPotentialRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Subtotal    
Total (160)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
(111)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityUndiscountedDirectAssumedNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Discount    
Total 34ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
51ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationReductionsofGrossClaimLiabilityNetofReinsuranceRecoverableDiscount
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Present value of expected cash flows    
Net expected loss to be paid (126)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
(60)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationNetClaimLiabilityNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Deferred premium revenue    
Total (116)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
(178)ago_ScheduleofInsuredFinancialObligationswithCreditDeteriorationStatementofFinancialPositionUnearnedPremiumRevenueNetofReinsuranceRecoverable
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Reserves (salvage)    
Total $ (79)ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
[4] $ (18)ago_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseNetofReinsuranceandSalvageSubrogationandOtherRecoveries
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
[4]
[1] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making Debt Service payments. The ceded number of risks represents the number of risks for which the Company ceded a portion of its exposure.
[2] Includes BIG amounts related to FG VIEs.
[3] Includes excess spread and draws on HELOCs.
[4] See table “Components of net reserves (salvage).”