XML 71 R51.htm IDEA: XBRL DOCUMENT
v3.22.1

Expected Loss to be Paid (Recovered) - Additional Information (Details) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2022 USD ($) Payment scenario Curve | Mar. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) scenario | Dec. 31, 2020 USD ($)
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Period of insured credit performance of guaranteed obligations (in some cases over) | 30 years |  |  |
Discount factor (as a percent) | 2.26% |  | 1.02% |
Net Expected Loss to be Paid (Recovered) | $ 432 | $ 472 | $ 411 | $ 529
Loss and LAE Reserve paid | 13 | 4 |  |
Expected LAE to be paid | 17 |  | 26 |
Ceded expected loss to be recovered (paid) | (2) |  | 10 |
Net par outstanding | 233,379 |  | 236,392 |
Net economic loss development (benefit) | $ (44) | 13 |  |
Additional loss recovery assumption, recovery period | 5 years |  |  |
Loss recovery assumption, additional increase in recovery projection, percent | 40.00% |  |  |
Loss recovery assumption, additional increase in recovery projection, economic benefit | $ 40 |  |  |
Loss recovery assumption, additional decrease in recovery projection, percent | 20.00% |  |  |
Loss recovery assumption, additional decrease in recovery projection, economic loss | $ 40 |  |  |
Public Finance Stockton Pension Obligation Bonds |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 100 |  |  |
Public finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | 191 | 252 | 209 | 341
Net par outstanding | 224,463 |  | 227,164 |
Net economic loss development (benefit) | (50) | 3 |  |
Other structured finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | 46 | 39 | 52 | 40
Net par outstanding | 6,639 |  | 6,837 |
Net economic loss development (benefit) | (1) | (1) |  |
BIG |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 5,639 |  | 7,356 |
BIG | Public finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 4,295 |  | 5,972 |
BIG | Other structured finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 115 |  | $ 119 |
BIG | Student Loan |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 53 |  |  |
BIG | Life insurance transactions |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | $ 40 |  |  |
UNITED STATES |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net expected loss to be paid after recoveries for representations and warranties, percent | 98.00% |  | 97.20% |
UNITED STATES | Public finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | $ 181 | 228 | $ 197 | 305
Net par outstanding | 175,957 |  | 177,219 |
Net economic loss development (benefit) | (48) | 15 |  |
UNITED STATES | RMBS |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | 195 | 181 | 150 | $ 148
Net par outstanding | 2,277 |  | 2,391 |
Net economic loss development (benefit) | $ 7 | 11 |  |
UNITED STATES | RMBS | Second Lien |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Period from plateau to intermediate conditional default rate (in months) | 28 months |  |  |
UNITED STATES | RMBS | Home Equity Line of Credit |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Final CPR | 1.00% |  |  |
UNITED STATES | RMBS | First Lien |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | $ 204 |  | $ 167 |
Net economic loss development (benefit) | $ 18 | 25 |  |
Number of delinquent payments | Payment | 2 |  |  |
Projected loss assumptions, CDR, plateau rate, projection period | 36 months |  |  |
Projected loss assumptions, final CPR, period for voluntary prepayments to continue | 12 months |  |  |
Percent of deferred loan balances to be recovered | 20.00% |  |  |
Intermediate conditional default rate (as a percent) | 5.00% |  |  |
Number of scenarios weighted in estimating expected losses | scenario | 5 |  | 5 |
UNITED STATES | RMBS | First Lien | Base Scenario |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Projected loss assumptions, CDR, plateau rate, projection period | 36 months |  |  |
Period from plateau to intermediate conditional default rate (in months) | 12 months |  |  |
Intermediate conditional default rate as a percentage of plateau conditional default rate | 20.00% |  |  |
Final conditional default rate as a percentage of plateau conditional default rate | 5.00% |  |  |
Projected loss assumptions, final CPR, period for voluntary prepayments to continue | 1 year 3 months |  |  |
Default from delinquentor rate, term | 36 months |  |  |
Performing or projected to reperform, projection period | 36 months |  |  |
Projected loss assumptions, loss severity, subsequent period | 18 months |  |  |
Estimated loss severity rate, one through six months (as a percent) | 18 months |  |  |
Loss severity (as a percent) | 40.00% |  |  |
Projected loss assumptions, period to reach final loss severity rate | 2 years 6 months |  |  |
Final CPR | 15.00% |  |  |
UNITED STATES | RMBS | First Lien | More Stressful Environment |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Period from plateau to intermediate conditional default rate (in months) | 15 months |  |  |
Projected loss assumptions, increase (decrease) in expected loss to be paid, net | $ (20) |  |  |
UNITED STATES | RMBS | First Lien | Least Stressful Environment |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Projected loss assumptions, CDR, plateau rate, projection period | 30 months |  |  |
Period from plateau to intermediate conditional default rate (in months) | 9 months |  |  |
Projected loss assumptions, increase (decrease) in expected loss to be paid, net | $ 12 |  |  |
Decrease in the plateau period used to calculate potential change in loss estimate (in months) | 6 months |  |  |
UNITED STATES | RMBS | First Lien | Most Stressful |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Projected loss assumptions, period to reach final loss severity rate | 9 years |  |  |
UNITED STATES | RMBS | Second Lien |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | $ (9) |  | $ 17 |
Net economic loss development (benefit) | $ (11) | $ (14) |  |
Period from plateau to intermediate conditional default rate (in months) | 28 months |  |  |
Period of loan default estimate | 6 months |  |  |
Number of preceding months average liquidation rates used to estimate loan default rate | 6 months |  |  |
Projected loss assumptions, period of consistent conditional default rate | 6 months |  |  |
Stress period (in months) | 34 months |  |  |
Monthly delinquency threshold | 6 months |  |  |
Loss recovery assumption (as a percent) | 2.00% |  | 2.00% |
Number of conditional default rate curves modeled in estimating losses | Curve | 5 |  |  |
Liquidation rate | 30.00% |  |  |
UNITED STATES | RMBS | Second Lien | Home Equity Line of Credit and Closed-end Mortgage |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Final CPR | 15.00% |  |  |
UNITED STATES | RMBS | Second Lien | Base Scenario |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Stress period (in months) | 34 months |  |  |
UNITED STATES | RMBS | Second Lien | Most Stressful |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Projected loss assumptions, CDR, plateau rate, projection period | 8 months |  |  |
Period from plateau to intermediate conditional default rate (in months) | 31 months |  |  |
Stress period (in months) | 39 months |  |  |
Increase in conditional default rate ramp down period | 3 months |  |  |
UNITED STATES | RMBS | Second Lien | Most Stressful | Home Equity Line of Credit |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Change in estimate for increased conditional default rate plateau period | $ 5 |  |  |
UNITED STATES | RMBS | Second Lien | Least Stressful |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Stress period (in months) | 29 months |  |  |
Period of constant conditional default rate (in months) | 4 months |  |  |
Decreased conditional default rate ramp down period | 25 months |  |  |
Change in estimate for decreased prepayment rate, Percent | 10.00% |  |  |
UNITED STATES | RMBS | Second Lien | Least Stressful | Home Equity Line of Credit |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Change in estimate for decreased conditional default rate ramp down period | $ 6 |  |  |
UNITED STATES | Home Equity Line of Credit |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Initial period for which borrower can pay only interest payments | 10 years |  |  |
UNITED STATES | BIG | Public finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | $ 3,734 |  | $ 5,372 |
UNITED STATES | BIG | RMBS |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 1,229 |  | 1,265 |
Puerto Rico |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 2,237 |  | 3,572 |
Puerto Rico | BIG |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net par outstanding | 2,237 |  | 3,572 |
Non United States | Public finance |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Net Expected Loss to be Paid (Recovered) | 10 |  | $ 12 |
Net economic loss development (benefit) | $ 2 |  |  |
Minimum |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Risk free discount rate | 0.00% |  | 0.00% |
Maximum |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |
Risk free discount rate | 2.61% |  | 1.98% |

X
- Definition Additional Loss Recovery Assumption, Recovery Period + References No definition available. + Details
Name: | ago_AdditionalLossRecoveryAssumptionRecoveryPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ceded Expected Loss to be Recovered (Paid) + References No definition available. + Details
Name: | ago_CededExpectedLossToBeRecoveredPaid
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the number of possible conditional default rate curves modeled and probability weighted in estimating loss on insured obligations. + References No definition available. + Details
Name: | ago_ConditionalDefaultRateNumberOfCurves
Namespace Prefix: | ago_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The period for which the conditional default rate of a pool of insured obligations is held constant, following the period for which default is estimated based on past due balances. + References No definition available. + Details
Name: | ago_ConditionalDefaultRatePlateauPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expected Loss Adjustment Expense To Be Paid + References No definition available. + Details
Name: | ago_ExpectedLossAdjustmentExpenseToBePaid
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the initial period over which defaults projected to occur on a pool of insured obligations represent defaults that can be attributed to obligations that are currently delinquent or in foreclosure. + References No definition available. + Details
Name: | ago_GuarantorObligationsDefaultPeriodFromDelinquent
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Guarantor Obligations, Net Expected Loss Development After Recoveries for Representations and Warranties + References No definition available. + Details
Name: | ago_GuarantorObligationsNetExpectedLossDevelopmentAfterRecoveriesforRepresentationsandWarranties
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties + References No definition available. + Details
Name: | ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarranties
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Guarantor Obligations, Net Expected Loss to be Paid After Recoveries for Representations and Warranties, Percent + References No definition available. + Details
Name: | ago_GuarantorObligationsNetExpectedLosstobePaidAfterRecoveriesforRepresentationsandWarrantiesPercent
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Guarantor Obligations, Projected Loss Assumption, Deferred Loan Balances to be Recovered, Percent + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionDeferredLoanBalancesToBeRecoveredPercent
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Guarantor Obligations, Projected Loss Assumption, Final Conditional Prepayment Rates, Final Rate, Term + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionFinalConditionalPrepaymentRatesFinalRateTerm
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Guarantor Obligations, Projected Loss Assumptions, Conditional Default Rate, Intermediate Rate + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsConditionalDefaultRateIntermediateRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Guarantor Obligations, Projected Loss Assumptions, Conditional Default Rate, Plateau Rate, Performing or Projected to Reperform, Projection Period + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsConditionalDefaultRatePlateauRatePerformingorProjectedtoReperformProjectionPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period over which the application of the constant conditional default rate would produce approximately the amount of defaults calculated for each delinquency category of insured financial obligations. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsConditionalDefaultRatePlateauRateProjectionPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the decrease in the conditional default rate plateau period for which the change in loss estimate for a pool of insured obligations is calculated. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsConditionalDefaultRatePlateauRateProjectionPeriodDecrease
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the final conditional default rate on a pool of insured obligations as a percentage of the plateau conditional default rate. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsFinalConditionalDefaultRateasPercentageofPlateauConditionalDefaultRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the change in expected loss on a pool of insured obligations that would result from an increase in the conditional default rate plateau period and loss severity recovery period. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsIncreaseDecreaseinExpectedLosstobePaidNet
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the intermediate conditional default rate on a pool of insured obligations as a percentage of the plateau conditional default rate. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsIntermediateConditionalDefaultRateasPercentageofPlateauConditionalDefaultRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Guarantor Obligations, Projected Loss Assumptions, Liquidation Rate + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsLiquidationRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Guarantor Obligations, Projected Loss Assumptions, Loss Severity, Initial Period + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsLossSeverityInitialPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the present value of the final level of assumed lifetime losses on a pool of insured obligations as a percentage of principal balance. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsLossSeverityRateFinalRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Guarantor Obligations, Projected Loss Assumptions, Loss Severity, Subsequent Period + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsLossSeveritySubsequentPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of scenarios used during the current period in estimation of expected loss on a pool of insured obligations. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsNumberofScenariosConsidered
Namespace Prefix: | ago_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Guarantor Obligations, Projected Loss Assumptions, Period Of Consistent Conditional Default Rate + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsPeriodOfConsistentConditionalDefaultRate
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period over which the conditional prepayment rate assumed for a pool of insured obligations trends from the initial to the final rate. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsPeriodtoReachFinalLossSeverityRate
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period over which the conditional default rate on a pool of insured obligations is assumed to improve from the current level to an intermediate conditional default rate. + References No definition available. + Details
Name: | ago_GuarantorObligationsProjectedLossAssumptionsPeriodtoReachIntermediateConditionalDefaultRate
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Initial Period for Which Borrower Can Pay Only Interest Payments + References No definition available. + Details
Name: | ago_InitialPeriodforWhichBorrowerCanPayOnlyInterestPayments
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Insured Financial Obligations, Claim Liability, Risk Free Discount Rate + References No definition available. + Details
Name: | ago_InsuredFinancialObligationsClaimLiabilityRiskFreeDiscountRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Insured Financial Obligations, Claim Liability, Weighted Average Risk Free Discount Rate + References No definition available. + Details
Name: | ago_InsuredFinancialObligationsClaimLiabilityWeightedAverageRiskFreeDiscountRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Insured Financial Obligations, Insured Credit Performance of Guaranteed Obligations, Term + References No definition available. + Details
Name: | ago_InsuredFinancialObligationsInsuredCreditPerformanceofGuaranteedObligationsTerm
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Insured Financial Obligations, Liability for Unpaid Claims Adjustment Expense, Claims Paid + References No definition available. + Details
Name: | ago_InsuredFinancialObligationsLiabilityforUnpaidClaimsAdjustmentExpenseClaimsPaid
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the outstanding principal amounts of the underlying insured obligations for financial guaranty contracts, after netting out ceded contracts. + References No definition available. + Details
Name: | ago_InsuredFinancialObligationsOutstandingPrincipalAmountNet
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Insured Financial Obligations, Projected Loss Assumptions, Conditional Prepayment Rate, Final Rate + References No definition available. + Details
Name: | ago_InsuredFinancialObligationsProjectedLossAssumptionsConditionalPrepaymentRateFinalRate
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the change in expected loss on a pool of insured obligations that would result from a decrease in the conditional default rate ramp period. + References No definition available. + Details
Name: | ago_LossEstimateSensitivityAnalysisChangeInEstimateForDecreasedConditionalDefaultRateRampDownPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Loss Estimate Sensitivity Analysis, Change In Estimate For Decreased Prepayment Rate, Percent + References No definition available. + Details
Name: | ago_LossEstimateSensitivityAnalysisChangeInEstimateForDecreasedPrepaymentRatePercent
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the change in expected loss on a pool of insured obligations that would result from an increase in the conditional default rate plateau period. + References No definition available. + Details
Name: | ago_LossEstimateSensitivityAnalysisChangeInEstimateForIncreasedConditionalDefaultRatePlateauPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the decreased conditional default rate ramp down period for which the change in loss estimate for a pool of insured obligations is calculated. + References No definition available. + Details
Name: | ago_LossEstimateSensitivityAnalysisDecreasedConditionalDefaultRateRampDownPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loss Estimate Sensitivity Analysis Increase in Conditional Default Rate Ramp Down Period + References No definition available. + Details
Name: | ago_LossEstimateSensitivityAnalysisIncreaseInConditionalDefaultRateRampDownPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of assumed lifetime losses on a pool of insured obligations that is anticipated to be recovered. + References No definition available. + Details
Name: | ago_LossRecoveryAssumption
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Loss Recovery Assumption, Additional Decrease in Recovery Projection, Economic Loss + References No definition available. + Details
Name: | ago_LossRecoveryAssumptionAdditionalDecreaseinRecoveryProjectionEconomicLoss
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Loss Recovery Assumption, Additional Decrease in Recovery Projection, Percent + References No definition available. + Details
Name: | ago_LossRecoveryAssumptionAdditionalDecreaseinRecoveryProjectionPercent
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Loss Recovery Assumption, Additional Increase in Recovery Projection, Economic Benefit + References No definition available. + Details
Name: | ago_LossRecoveryAssumptionAdditionalIncreaseinRecoveryProjectionEconomicBenefit
Namespace Prefix: | ago_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Loss Recovery Assumption, Additional Increase in Recovery Projection, Percent + References No definition available. + Details
Name: | ago_LossRecoveryAssumptionAdditionalIncreaseinRecoveryProjectionPercent
Namespace Prefix: | ago_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Monthly Delinquency Threshold, Period + References No definition available. + Details
Name: | ago_MonthlyDelinquencyThresholdPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Preceding Months Liquidation Rates Used to Estimate Loan Default Rate + References No definition available. + Details
Name: | ago_NumberOfPrecedingMonthsLiquidationRatesUsedToEstimateLoanDefaultRate
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Delinquent Payments + References No definition available. + Details
Name: | ago_NumberofDelinquentPayments
Namespace Prefix: | ago_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period for which the entity estimates the number of insured obligations that will default. + References No definition available. + Details
Name: | ago_PeriodofDefaultEstimate
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition [Line Items] for Schedule of Expected Losses to be Paid [Table] + References No definition available. + Details
Name: | ago_ScheduleofExpectedLossestobePaidLineItems
Namespace Prefix: | ago_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the total stress period. + References No definition available. + Details
Name: | ago_TotalStressPeriod
Namespace Prefix: | ago_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_UnderlyingAssetClassAxis=ago_PublicFinanceStocktonPensionObligationBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnderlyingAssetClassAxis=ago_PublicFinanceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnderlyingAssetClassAxis=ago_OtherStructuredFinanceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InternalCreditAssessmentAxis=us-gaap_InternalNoninvestmentGradeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnderlyingAssetClassAxis=us-gaap_StudentLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnderlyingAssetClassAxis=ago_LifeInsuranceTransactionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_MortgageLoansOnRealEstateLoanTypeAxis=us-gaap_SecondMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=us-gaap_FirstMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=ago_BaseScenarioMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=ago_MoreStressfulEnvironmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=ago_LeastStressfulEnvironmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=ago_BaseScenarioOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionLoanCategoryAxis=us-gaap_SecondMortgageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | srt_StatementScenarioAxis=ago_BasedScenarioTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_UnderlyingAssetClassAxis=us-gaap_HomeEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_PR
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=ago_NonUnitedStatesMember
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: |