XML 107 R83.htm IDEA: XBRL DOCUMENT
v3.24.1.u1

Fair Value Measurement - Quantitative Information - Assets & Liabilities (Details) - Level 3 - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 | Dec. 31, 2023
Credit derivative liabilities, net |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Internal floor (in bps) | 0.00100 | 0.00100
Valuation, Income Approach | Credit derivative liabilities, net |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value | $ (39) | $ (50)
Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Fair value | $ (399) | $ (554)
Minimum | Credit derivative liabilities, net |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Hedge cost (in bps) | 0.087% | 0.102%
Bank profit (as a percent) | 0.836% | 1.056%
Minimum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 4.80% | 5.00%
Maximum | Credit derivative liabilities, net |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Hedge cost (in bps) | 0.206% | 0.265%
Bank profit (as a percent) | 2.683% | 3.026%
Maximum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 10.80% | 10.70%
Weighted Average | Credit derivative liabilities, net |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Hedge cost (in bps) | 0.125% | 0.158%
Bank profit (as a percent) | 1.394% | 1.586%
Weighted Average | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 5.90% | 5.80%
CPR | Minimum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 0.20% | 0.20%
CPR | Maximum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 21.60% | 21.40%
CPR | Weighted Average | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 7.60% | 7.80%
CDR | Minimum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 1.30% | 1.30%
CDR | Maximum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 41.00% | 41.00%
CDR | Weighted Average | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 10.50% | 10.40%
Loss severity | Minimum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 45.00% | 45.00%
Loss severity | Maximum | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 100.00% | 100.00%
Loss severity | Weighted Average | Valuation, Income Approach | FG VIEs' assets |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 82.90% | 82.90%
Obligations of state and political subdivisions | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 6 | $ 6
Obligations of state and political subdivisions | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.00% | 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% | 22.50%
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% | 7.80%
RMBS | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 153 | $ 154
RMBS | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.60% | 7.50%
RMBS | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 11.40% | 11.30%
RMBS | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 9.00% | 8.90%
RMBS | CPR | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 0.90% | 0.10%
RMBS | CPR | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 15.00% | 15.00%
RMBS | CPR | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 3.20% | 3.40%
RMBS | CDR | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 1.50% | 1.50%
RMBS | CDR | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 18.80% | 18.80%
RMBS | CDR | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 5.70% | 5.60%
RMBS | Loss severity | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 50.00% | 50.00%
RMBS | Loss severity | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 125.00% | 125.00%
RMBS | Loss severity | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 81.60% | 82.60%
CLOs | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 439 | $ 450
CLOs | Discount margin | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 1.00% | 1.10%
CLOs | Discount margin | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 9.60% | 9.50%
CLOs | Discount margin | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 2.50% | 2.60%
Others | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 382 | $ 353
Others | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 6.60% | 6.20%
Others | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 10.10% | 11.70%
Others | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.80% | 7.80%
FG VIEs' assets | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 167 | $ 174
FG VIEs' assets | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 5.70% | 5.50%
FG VIEs' assets | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 10.80% | 10.90%
FG VIEs' assets | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 9.50% | 9.40%
FG VIEs' assets | CPR | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 0.20% | 0.20%
FG VIEs' assets | CPR | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 21.60% | 21.40%
FG VIEs' assets | CPR | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 7.60% | 7.80%
FG VIEs' assets | CDR | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 1.30% | 1.30%
FG VIEs' assets | CDR | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 41.00% | 41.00%
FG VIEs' assets | CDR | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 10.50% | 10.40%
FG VIEs' assets | Loss severity | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 45.00% | 45.00%
FG VIEs' assets | Loss severity | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 100.00% | 100.00%
FG VIEs' assets | Loss severity | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 82.90% | 82.90%
Structured products | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 9.80% |
Structured products | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 23.50% |
Structured products | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 16.60% |
Other assets | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 3 | $ 13
Term (years) | 10 years | 10 years
Other assets | Minimum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.50% | 14.70%
Year 1 loss estimates |  | 7.80%
Other assets | Maximum | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 8.00% | 21.40%
Year 1 loss estimates |  | 8.40%
Other assets | Weighted Average | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 7.80% | 18.00%
Year 1 loss estimates |  | 8.10%
Consolidated Investment Vehicles | Valuation, Income Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 89 | $ 80
Consolidated Investment Vehicles | Valuation, Income Approach | Structured products |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 220 | $ 189
Consolidated Investment Vehicles | Discount margin | Valuation, Income Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) |  | 20.90%
Consolidated Investment Vehicles | Discount margin | Minimum | Valuation, Income Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 16.50% |
Consolidated Investment Vehicles | Discount margin | Maximum | Valuation, Income Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 23.50% |
Consolidated Investment Vehicles | Discount margin | Weighted Average | Valuation, Income Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 20.50% |
Consolidated Investment Vehicles | Terminal growth rate | Valuation, Income Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 4.00% | 4.00%
Consolidated Investment Vehicles | Measurement input, revenue multiple | Valuation, Market Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Market multiple-price to book | 105.00% | 110.00%
Exit multiple-price to earnings | 525.00% | 550.00%
Consolidated Investment Vehicles | Exit multiple-price to book | Valuation, Market Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 110.00% | 110.00%
Consolidated Investment Vehicles | Exit multiple-price to earnings | Valuation, Market Approach | Equity securities |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Yield (as a percent) | 525.00% | 550.00%
Other invested assets | Valuation, Income Approach |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Total assets carried at fair value | $ 4 | $ 3

X
- Definition Represents the bank profit (in basis points), used as an input to measure fair value. + References No definition available. + Details
Name: | ago_FairValueInputsBankProfit
Namespace Prefix: | ago_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the hedge cost (in basis points), used as an input to measure fair value. + References No definition available. + Details
Name: | ago_FairValueInputsHedgeCost
Namespace Prefix: | ago_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair Value Inputs Internal Floor + References No definition available. + Details
Name: | ago_FairValueInputsInternalFloor
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 Year One Loss Estimate + References No definition available. + Details
Name: | ago_FairValueYearOneLossEstimate
Namespace Prefix: | ago_
Data Type: | dtr-types: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
- Definition Fair value of financial and nonfinancial obligations. + 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_LiabilitiesFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
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_FairValueByLiabilityClassAxis=ago_FinancialGuaranteeVariableInterestEntitiesMember
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_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_FairValueByAssetClassAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
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_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
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_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_ConsolidatedInvestmentVehiclesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
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_MeasurementInputTypeAxis=us-gaap_MeasurementInputLongTermRevenueGrowthRateMember
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=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_FairValueByAssetClassAxis=ago_OtherInvestedAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |