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Outstanding Exposure - Amortization Schedule of Puerto Rico BIG Net Par Outstanding and BIG Net Debt Service Outstanding (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Estimated BIG Net Par Amortization [Abstract]    
Net Par Outstanding (excluding loss mitigation bonds) $ 389,099.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet [1] $ 403,729.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet [2]
Estimated BIG Net Debt Service Amortization [Abstract]    
Total 584,659ago_InsuredFinancialObligationsInsuredContractualPaymentsOutstandingNet 609,622ago_InsuredFinancialObligationsInsuredContractualPaymentsOutstandingNet
Puerto Rico [Member]    
Estimated BIG Net Par Amortization [Abstract]    
Net Par Outstanding (excluding loss mitigation bonds) 4,940.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_StatementGeographicalAxis
= country_PR		 4,939.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_StatementGeographicalAxis
= country_PR
BIG [Member]    
Estimated BIG Net Par Amortization [Abstract]    
Net Par Outstanding (excluding loss mitigation bonds) 17,860.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember		 18,247.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
BIG [Member] | Puerto Rico [Member]    
Estimated BIG Net Par Amortization [Abstract]    
2015 (April 1 - June 30) 0ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountFirstQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (July 1 - September 30) 297ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountSecondQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (October 1 - December 31) 33ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountThirdQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2016 267ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwo
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2017 207ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearThree
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2018 157ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearFour
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2019 187ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2020 255ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSix
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2021 109ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSeven
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2022 110ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearEight
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2023 141ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearNine
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2024 160ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2025-2029 916ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearEleventoFifteen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2030-2034 827ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSixteentoTwenty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2035-2039 669ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwentyOnetoTwentyFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2040-2044 90ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwentySixtoThirty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2045-2047 246ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountThereafter
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Net Par Outstanding (excluding loss mitigation bonds) 4,671.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Estimated BIG Net Debt Service Amortization [Abstract]    
2015 (April 1 - June 30) 3ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsFirstQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (July 1 - September 30) 413ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsSecondQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (October 1 - December 31) 37ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsThirdQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2016 487ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwo
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2017 415ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearThree
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2018 353ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearFour
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2019 375ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2020 434ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSix
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2021 274ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSeven
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2022 269ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearEight
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2023 297ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearNine
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2024 309ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2025-2029 1,517ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearEleventoFifteen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2030-2034 1,238ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSixteentoTwenty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2035-2039 829ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwentyOnetoTwentyFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2040-2044 159ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwentySixtoThirty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2045-2047 272ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsThereafter
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Total 7,681ago_InsuredFinancialObligationsInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]    
Estimated BIG Net Par Amortization [Abstract]    
Net Par Outstanding (excluding loss mitigation bonds) 2,448.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		 2,447.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR
Subject to the Terms of the Recovery Act [Member] | BIG [Member] | Puerto Rico [Member]    
Estimated BIG Net Par Amortization [Abstract]    
2015 (April 1 - June 30) 0ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountFirstQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (July 1 - September 30) 126ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountSecondQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (October 1 - December 31) 0ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountThirdQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2016 84ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwo
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2017 41ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearThree
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2018 48ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearFour
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2019 61ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2020 73ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSix
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2021 51ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSeven
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2022 43ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearEight
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2023 102ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearNine
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2024 82ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2025-2029 576ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearEleventoFifteen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2030-2034 440ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSixteentoTwenty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2035-2039 397ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwentyOnetoTwentyFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2040-2044 78ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwentySixtoThirty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2045-2047 246ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountThereafter
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Net Par Outstanding (excluding loss mitigation bonds) 2,448.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Estimated BIG Net Debt Service Amortization [Abstract]    
2015 (April 1 - June 30) 2ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsFirstQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (July 1 - September 30) 186ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsSecondQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (October 1 - December 31) 2ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsThirdQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2016 200ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwo
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2017 153ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearThree
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2018 158ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearFour
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2019 168ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2020 176ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSix
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2021 151ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSeven
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2022 140ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearEight
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2023 198ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearNine
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2024 173ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2025-2029 951ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearEleventoFifteen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2030-2034 696ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSixteentoTwenty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2035-2039 525ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwentyOnetoTwentyFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2040-2044 146ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwentySixtoThirty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2045-2047 272ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsThereafter
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Total 4,297ago_InsuredFinancialObligationsInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_SubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]    
Estimated BIG Net Par Amortization [Abstract]    
Net Par Outstanding (excluding loss mitigation bonds) 2,492.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		 2,492.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR
Not Subject to the Terms of the Recovery Act [Member] | BIG [Member] | Puerto Rico [Member]    
Estimated BIG Net Par Amortization [Abstract]    
2015 (April 1 - June 30) 0ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountFirstQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (July 1 - September 30) 171ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountSecondQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (October 1 - December 31) 33ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountThirdQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2016 183ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwo
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2017 166ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearThree
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2018 109ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearFour
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2019 126ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2020 182ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSix
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2021 58ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSeven
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2022 67ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearEight
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2023 39ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearNine
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2024 78ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2025-2029 340ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearEleventoFifteen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2030-2034 387ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearSixteentoTwenty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2035-2039 272ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwentyOnetoTwentyFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2040-2044 12ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountYearTwentySixtoThirty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2045-2047 0ago_InsuredFinancialObligationsMaturitiesofOutstandingPrincipalAmountThereafter
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Net Par Outstanding (excluding loss mitigation bonds) 2,223.0ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Estimated BIG Net Debt Service Amortization [Abstract]    
2015 (April 1 - June 30) 1ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsFirstQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (July 1 - September 30) 227ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsSecondQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2015 (October 1 - December 31) 35ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsThirdQuarterAfterPeriodEnd
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2016 287ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwo
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2017 262ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearThree
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2018 195ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearFour
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2019 207ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2020 258ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSix
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2021 123ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSeven
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2022 129ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearEight
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2023 99ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearNine
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2024 136ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2025-2029 566ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearEleventoFifteen
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2030-2034 542ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearSixteentoTwenty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2035-2039 304ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwentyOnetoTwentyFive
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2040-2044 13ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsYearTwentySixtoThirty
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
2045-2047 0ago_InsuredFinancialObligationsMaturitiesofOutstandingContractualPaymentsThereafter
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
/ us-gaap_StatementGeographicalAxis
= country_PR		  
Total $ 3,384ago_InsuredFinancialObligationsInsuredContractualPaymentsOutstandingNet
/ us-gaap_InternalCreditAssessmentAxis
= ago_InternalNoninvestmentGradeMember
/ us-gaap_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationBySurveillanceCategoryAxis
= ago_NotSubjecttotheTermsoftheRecoveryActMember
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= country_PR		  
[1] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of March 31, 2015, which are primarily in the BIG category.
[2] Excludes $1.3 billion of loss mitigation securities insured and held by the Company as of December 31, 2014, which are primarily in the BIG category.