XML 99 R88.htm IDEA: XBRL DOCUMENT
v3.23.2

Fair Value Measurement - Narrative (Details) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2023 USD ($) Security Trust | Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Repurchase agreement liability | $ 36 | $ 35
Assured IM |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Obligation to purchase debt | 0.05 |
Total |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Percentage of CDS contracts fair valued Using minimum premium | 10.60% |
AGC And AGM |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Number of custodial trusts | Trust | 4 |
Share value, amount | $ 200 |
Maximum amount | $ 50 |
Recurring | Level 3 |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Number of fixed maturity securities valued using model processes | Security | 193 |
Recurring | Level 3 | CDR | Total | Minimum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 2.94% | 2.78%
Recurring | Level 3 | CDR | Total | Maximum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 5.48% | 5.08%

X
- Definition Represents the number of fixed maturity securities and short-term investments which have been valued using model processes set by the entity. + References No definition available. + Details
Name: | ago_AvailableforsaleDebtSecuritiesNumberofInstruments
Namespace Prefix: | ago_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of custodial trusts with whom the entity entered into put agreements. + References No definition available. + Details
Name: | ago_FinancialInstrumentsSubjecttoMandatoryRedemptionSettlementTermsNumberofCustodialTrusts
Namespace Prefix: | ago_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Obligation, Debt Purchase, Percent + References No definition available. + Details
Name: | ago_ObligationDebtPurchasePercent
Namespace Prefix: | ago_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of CDS Contracts Fair Valued Using Minimum Premium + References No definition available. + Details
Name: | ago_PercentageOfCDSContractsFairValuedUsingMinimumPremium
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(m)(1)(i)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(m)(1)(ii)(A)(ii)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1 + Details
Name: | us-gaap_AssetsSoldUnderAgreementsToRepurchaseRepurchaseLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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 Amount that would be paid, determined under the conditions specified in the contract, if the holder of the share has the right to redeem the shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481648/480-10-50-2 + Details
Name: | us-gaap_SharesSubjectToMandatoryRedemptionSettlementTermsAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The maximum amount that the issuer could be required to pay to redeem the instrument by physical settlement, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481648/480-10-50-2 + Details
Name: | us-gaap_SharesSubjectToMandatoryRedemptionSettlementTermsMaximumAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ago_AssuredIMMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CreditDerivativesByContractTypeAxis=us-gaap_CreditDefaultSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=ago_AGCAndAGMMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
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: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDefaultRateMember
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: |