XML 148 R92.htm IDEA: XBRL DOCUMENT v2.4.1.9
- Fair Value Level 3 Rollforward Recurring Basis (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
FG VIEs' liabilities with recourse, at fair value [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value at beginning of period $ (1,790)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 $ (2,090)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
Net income (loss) 94us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 [1],[2] (166)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 [1],[2]
Other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 [1] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 [1]
Purchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
Settlements 374us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 343us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
FG VIE consolidations (189)ago_FairValueMeasuredwithUnobservableInputsReconciliationRecurringBasisLiabilityConsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 (12)ago_FairValueMeasuredwithUnobservableInputsReconciliationRecurringBasisLiabilityConsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
FG VIE deconsolidations 234ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityDeconsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 135ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityDeconsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
Fair value at end of period (1,277)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 (1,790)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
Change in unrealized gains/(losses) related to financial instruments held (22)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember		 (169)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithRecourseMember
FG VIEs' liabilities without recourse, at fair value [Member]    
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Fair value at beginning of period (1,081)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 (1,051)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
Net income (loss) (43)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 [1],[2] (225)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 [1],[2]
Other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 [1] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInOtherComprehensiveIncome
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 [1]
Purchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
Settlements 22us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 168us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
FG VIE consolidations (42)ago_FairValueMeasuredwithUnobservableInputsReconciliationRecurringBasisLiabilityConsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 (37)ago_FairValueMeasuredwithUnobservableInputsReconciliationRecurringBasisLiabilityConsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
FG VIE deconsolidations 1,002ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityDeconsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 64ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityDeconsolidation
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
Fair value at end of period (142)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 (1,081)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
Change in unrealized gains/(losses) related to financial instruments held 3us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember		 (326)us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByLiabilityClassAxis
= ago_FinancialGuarantyVariableInterestLiabilitiesWithoutRecourseMember
Credit Risk Contract [Member]    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Fair value at beginning of period (1,693)us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] (1,793)us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
Net income (loss) 823us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [1],[3],[4] 65us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [1],[3],[4]
Other comprehensive income (loss) 0us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [1],[3] 0us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [1],[3]
Purchases 0us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchases
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] 0us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationPurchases
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
Settlements (25)us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationSettlements
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] 35us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationSettlements
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
FG VIE consolidations 0ago_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisUnobservableInputsReconciliationConsolidations
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] 0ago_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisUnobservableInputsReconciliationConsolidations
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
FG VIE deconsolidations 0ago_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisUnobservableInputsReconciliationDeconsolidations
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] 0ago_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisUnobservableInputsReconciliationDeconsolidations
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
Fair value at end of period (895)us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] (1,693)us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
Change in unrealized gains/(losses) related to financial instruments held 254ago_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisChangeinUnrealizedGainLoss
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3] (139)ago_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisChangeinUnrealizedGainLoss
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditRiskContractMember		 [3]
Obligations of state and political subdivisions [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 36us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 35us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Net Income (loss) 4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1],[5] (8)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1],[5]
Other comprehensive income (loss) (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1] 13us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1]
Purchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Settlements (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 (4)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
FG VIE Consolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
FG VIE deconsolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
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Fair value at end of period 38us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 36us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
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= us-gaap_USStatesAndPoliticalSubdivisionsMember
Change in unrealized gains/(losses) related to financial instruments held (1)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 14us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Corporate securities [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 136us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Net Income (loss) (46)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1],[5] 4us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1],[5]
Other comprehensive income (loss) (6)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Purchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 130us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 [6]
Settlements (5)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 (3)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
FG VIE Consolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
FG VIE deconsolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair value at end of period 79us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Change in unrealized gains/(losses) related to financial instruments held (6)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= us-gaap_CorporateDebtSecuritiesMember
RMBS [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 290us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 219us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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Net Income (loss) 21us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Other comprehensive income (loss) 24us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] 26us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
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Purchases 263us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Settlements (59)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 (54)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
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FG VIE Consolidations (127)ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
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FG VIE deconsolidations 13ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
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Fair value at end of period 425us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 290us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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Change in unrealized gains/(losses) related to financial instruments held 21us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Asset-backed Securities [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 268us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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Net Income (loss) 17us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Other comprehensive income (loss) 5us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
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Purchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
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Settlements (62)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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FG VIE Consolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
FG VIE deconsolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= us-gaap_AssetBackedSecuritiesMember
Fair value at end of period 228us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Other invested assets [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 2us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Net Income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_OtherInvestedAssetsMember
FG VIE Consolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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FG VIE deconsolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
= ago_OtherInvestedAssetsMember		 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetDeconsolidations
/ us-gaap_FairValueByAssetClassAxis
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Fair value at end of period 78us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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FG VIEs' assets, at fair value [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 2,565us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Net Income (loss) 164us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Purchases 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_VariableInterestEntityAssetsMember
Settlements (408)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_VariableInterestEntityAssetsMember
FG VIE Consolidations 206ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_VariableInterestEntityAssetsMember
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_VariableInterestEntityAssetsMember
Fair value at end of period 1,398us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Other assets [Member]    
Fair Value Level 3 Rollforward    
Fair value at beginning of period 46us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Other comprehensive income (loss) 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Settlements 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_OtherAssetBackedSecuritiesMember
FG VIE Consolidations 0ago_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisAssetConsolidations
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_OtherAssetBackedSecuritiesMember
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
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Fair value at end of period 35us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_OtherAssetBackedSecuritiesMember
Change in unrealized gains/(losses) related to financial instruments held $ (11)us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_FairValueByAssetClassAxis
= ago_OtherAssetBackedSecuritiesMember
[1] Realized and unrealized gains (losses) from changes in values of Level 3 financial instruments represent gains (losses) from changes in values of those financial instruments only for the periods in which the instruments were classified as Level 3.
[2] Included in fair value gains (losses) on FG VIEs.
[3] Represents net position of credit derivatives. The consolidated balance sheet presents gross assets and liabilities based on net counterparty exposure.
[4] Reported in net change in fair value of credit derivatives.
[5] Included in net realized investment gains (losses) and net investment income.
[6] Non-cash transaction.
[7] Reported in other income.
[8] Recorded in fair value gains (losses) on CCS.