XML 139 R117.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Fair Value Measurement - Quantitative Information - Assets (Details) - Level 3 - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Obligations of state and political subdivisions | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 6 | $ 47
Obligations of state and political subdivisions | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.40% | 7.40%
Obligations of state and political subdivisions | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 22.50% | 13.50%
Obligations of state and political subdivisions | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.80% | 9.40%
RMBS | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 154 | $ 179
RMBS | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.50% | 7.50%
RMBS | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 11.30% | 11.30%
RMBS | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 8.90% | 9.00%
CLO contracts | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 450 | $ 428
Others | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 353 | $ 366
Others | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 6.20% | 7.40%
Others | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 11.70% | 12.90%
Others | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.80% | 11.40%
Financial Guarantee Variable Interest Entities | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 174 | $ 204
Financial Guarantee Variable Interest Entities | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 5.50% | 6.60%
Financial Guarantee Variable Interest Entities | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 10.90% | 10.90%
Financial Guarantee Variable Interest Entities | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 9.40% | 7.50%
Consolidated Investment Vehicles | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 80 | $ 297
Yield (as a percent) |  | 10.00%
Consolidated Investment Vehicles | Valuation, Income Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 16.30%
Consolidated Investment Vehicles | Valuation, Income Approach | Structured products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 189 | $ 46
Consolidated Investment Vehicles | Minimum | Valuation, Income Approach | Structured products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 14.70% | 1280.00%
Consolidated Investment Vehicles | Maximum | Valuation, Income Approach | Structured products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 21.40% | 3710.00%
Consolidated Investment Vehicles | Weighted Average | Valuation, Income Approach | Structured products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 18.00% | 1890.00%
Other | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 13 | $ 47
Fair value inputs term | 10 years | 10 years
Other | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.80% | 7.70%
Other | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 8.40% | 8.40%
Other | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 8.10% | 8.10%
Other invested assets | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value | $ 3 | $ 5
CPR | RMBS | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 0.10% | 3.80%
CPR | RMBS | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 15.00% | 16.10%
CPR | RMBS | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 3.40% | 8.20%
CPR | Financial Guarantee Variable Interest Entities | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 0.20% | 0.90%
CPR | Financial Guarantee Variable Interest Entities | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 21.40% | 21.90%
CPR | Financial Guarantee Variable Interest Entities | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 7.80% | 12.90%
CDR | RMBS | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 1.50% | 1.50%
CDR | RMBS | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 18.80% | 12.00%
CDR | RMBS | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 5.60% | 5.90%
CDR | Financial Guarantee Variable Interest Entities | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 1.30% | 1.30%
CDR | Financial Guarantee Variable Interest Entities | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 41.00% | 41.00%
CDR | Financial Guarantee Variable Interest Entities | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 10.40% | 7.60%
Loss severity | RMBS | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 50.00% | 50.00%
Loss severity | RMBS | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 125.00% | 125.00%
Loss severity | RMBS | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 82.60% | 82.50%
Loss severity | Financial Guarantee Variable Interest Entities | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 45.00% | 45.00%
Loss severity | Financial Guarantee Variable Interest Entities | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 100.00% | 100.00%
Loss severity | Financial Guarantee Variable Interest Entities | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate (as a percent) | 82.90% | 81.00%
Measurement Input, Discount Rate | Valuation, Income Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Asset, fair value |  | $ 96
Measurement Input, Discount Rate | Minimum | Valuation, Income Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 20.80%
Measurement Input, Discount Rate | Maximum | Valuation, Income Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 23.80%
Measurement Input, Discount Rate | Weighted Average | Valuation, Income Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 21.70%
Measurement Input, Discount Rate | CLO contracts | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 1.10% | 1.80%
Measurement Input, Discount Rate | CLO contracts | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 9.50% | 4.10%
Measurement Input, Discount Rate | CLO contracts | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 2.60% | 3.00%
Measurement Input, Discount Rate | Consolidated Investment Vehicles | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 20.90% |
Measurement Input, Discount Rate | Consolidated Investment Vehicles | Minimum | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 19.80%
Measurement Input, Discount Rate | Consolidated Investment Vehicles | Maximum | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 25.10%
Measurement Input, Discount Rate | Consolidated Investment Vehicles | Weighted Average | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 22.70%
Multiple enterprise/revenue value | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple-price to earnings |  | 1.05
Multiple enterprise/revenue value | Consolidated Investment Vehicles | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Exit multiple-price to book | 110.00% | 115.00%
Exit multiple-price to earnings | 550.00% |
Multiple enterprise/revenue value | Consolidated Investment Vehicles | Minimum | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Exit multiple-price to earnings |  | 450.00%
Multiple enterprise/revenue value | Consolidated Investment Vehicles | Maximum | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple-price to earnings |  | 1.10
Multiple enterprise/revenue value | Consolidated Investment Vehicles | Weighted Average | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple-price to earnings |  | 1.08
Measurement Input, EBITDA Multiple | Minimum | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple - enterprise value/EBITDA |  | 2.50
Measurement Input, EBITDA Multiple | Maximum | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple - enterprise value/EBITDA |  | 11.00
Measurement Input, EBITDA Multiple | Weighted Average | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple - enterprise value/EBITDA |  | 10.25
Measurement Input, EBITDA Multiple | Consolidated Investment Vehicles | Minimum | Valuation, Market Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple - enterprise value/EBITDA |  | 2.5
Measurement Input, EBITDA Multiple | Consolidated Investment Vehicles | Maximum | Valuation, Market Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple - enterprise value/EBITDA |  | 2.75
Measurement Input, EBITDA Multiple | Consolidated Investment Vehicles | Weighted Average | Valuation, Market Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple - enterprise value/EBITDA |  | 2.63
Measurement Input, Long-Term Revenue Growth Rate | Consolidated Investment Vehicles | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 4.00% |
Measurement Input, Long-Term Revenue Growth Rate | Consolidated Investment Vehicles | Minimum | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 300.00%
Measurement Input, Long-Term Revenue Growth Rate | Consolidated Investment Vehicles | Maximum | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 400.00%
Measurement Input, Long-Term Revenue Growth Rate | Consolidated Investment Vehicles | Weighted Average | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 350.00%
Measurement Input, Exit Multiple, EBITDA | Consolidated Investment Vehicles | Valuation, Market Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 800.00%
Measurement Input, Exit Multiple, EBITDA | Consolidated Investment Vehicles | Minimum | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 800.00%
Measurement Input, Exit Multiple, EBITDA | Consolidated Investment Vehicles | Maximum | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 1200.00%
Measurement Input, Exit Multiple, EBITDA | Consolidated Investment Vehicles | Weighted Average | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 1053.00%
Measurement Input, Price to Book | Consolidated Investment Vehicles | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 130.00%
Measurement Input, Price to Earnings | Consolidated Investment Vehicles | Valuation, Market Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 550.00%
Market multiple-price to earnings | 5.50 |
Measurement Input, Cost to Sell | Consolidated Investment Vehicles | Valuation, Income Approach | Equity securities and warrants |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 100.00%
Measurement Input, Cost to Sell | Consolidated Investment Vehicles | Valuation, Income Approach | Corporate securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 100.00%

X
- Definition Fair Value Inputs, Market Multiple, Enterprise Value, EBITDA + References No definition available. + Details
Name: | ago_FairValueInputsMarketMultipleEnterpriseValueEBITDA
Namespace Prefix: | ago_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair Value Inputs, Market Multiple, Enterprise Value, Revenue + References No definition available. + Details
Name: | ago_FairValueInputsMarketMultipleEnterpriseValueRevenue
Namespace Prefix: | ago_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the term used as an input to measure fair value. + References No definition available. + Details
Name: | ago_FairValueInputsTerm
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the yield used as an input to measure fair value. + References No definition available. + Details
Name: | ago_FairValueInputsYield
Namespace Prefix: | ago_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair Value, Market Multiple, Price to Book + References No definition available. + Details
Name: | ago_FairValueMarketMultiplePriceToBook
Namespace Prefix: | ago_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair Value, Market Multiple, Price to Earnings + References No definition available. + Details
Name: | ago_FairValueMarketMultiplePriceToEarnings
Namespace Prefix: | ago_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Estimated rate of prepayment of principal on financial assets for initial fair value measurement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 860 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c)(2) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481326/860-20-50-3 + Details
Name: | us-gaap_AssumptionForFairValueOnSecuritizationDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesPrepaymentSpeed
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=us-gaap_IncomeApproachValuationTechniqueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_CollateralizedLoanObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=ago_OtherAssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=ago_FinancialGuaranteeVariableInterestEntitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=ago_ConsolidatedInvestmentVehiclesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=ago_EquitySecuritiesandWarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=ago_StructuredProductsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_OtherAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=ago_OtherInvestedAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputPrepaymentRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDefaultRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputLossSeverityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputRevenueMultipleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputEbitdaMultipleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputLongTermRevenueGrowthRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=ago_MeasurementInputExitMultipleEBITDAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=ago_MeasurementInputPriceToBookMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=ago_MeasurementInputPriceToEarningsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputCostToSellMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |