Name:	ago_AssetsToBePlacedInTrustForPaymentObligations
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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.

No definition available.

Name:	ago_ConditionalDefaultRateIntermediateStressPeriod
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Represents the period for which estimated default rates for a pool of insured obligations are calculated.

No definition available.

Name:	ago_DefaultEstimateLiquidationPeriod
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Estimated Loss Severity Rate, One through Six Months After Period End

No definition available.

Name:	ago_EstimatedLossSeverityRateOneThroughSixMonthsAfterPeriodEnd
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Estimated Loss Severity Rate, Six Through Twelve Months After Period End

No definition available.

Name:	ago_EstimatedLossSeverityRateSixThroughTwelveMonthsAfterPeriodEnd
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the final conditional default rate on a pool of insured obligations as a percentage of the plateau conditional default rate.

No definition available.

Name:	ago_FinalConditionalDefaultRateAsPercentageOfPlateauConditionalDefaultRate1
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

For financial guaranty insurance contracts, represents the recoveries during the period on defaulted insured obligations with breached representations and warranties plus the reduction to estimated losses from additional anticipated recoveries under a negotiated agreement.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsTotalRecoveriesUnderNegotiatedAgreement
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the intermediate conditional default rate on a pool of insured obligations as a percentage of the plateau conditional default rate.

No definition available.

Name:	ago_IntermediateConditionalDefaultRateAsPercentageOfPlateauConditionalDefaultRate
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The period for which the intermediate conditional default rate on a pool of insured obligations is held constant.

No definition available.

Name:	ago_IntermediateConditionalDefaultRateConstantPeriod
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Represents the liquidation rate used to estimate the number of insured obligations in the 30 - 59 days delinquent loan category that will default.

No definition available.

Name:	ago_LiquidationRateFor30To59DaysDelinquentCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the liquidation rate used to estimate the number of insured obligations in the 60 - 89 days delinquent loan category that will default.

No definition available.

Name:	ago_LiquidationRateFor60To89DaysDelinquentCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the liquidation rate used to estimate the number of insured obligations in the 90 or more days delinquent loan category that will default.

No definition available.

Name:	ago_LiquidationRateFor90OrMoreDaysDelinquentCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the liquidation rate used to estimate the number of insured obligations in the bankruptcy delinquent loan category that will default.

No definition available.

Name:	ago_LiquidationRateForBankruptcyDelinquentCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the liquidation rate used to estimate the number of insured obligations in foreclosure that will default.

No definition available.

Name:	ago_LiquidationRateForForeclosureCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the liquidation rate used to estimate the number of insured obligations related to real estate owned by the entity that will default.

No definition available.

Name:	ago_LiquidationRateForRealEstateOwnedCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the present value of the final level of assumed lifetime losses on a pool of insured obligations as a percentage of principal balance.

No definition available.

Name:	ago_LossSeverityFinal
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the period over which the loss severity is assumed to decline to a final level.

No definition available.

Name:	ago_LossSeverityRecoveryPeriod
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Represents the minimum percentage of mortgage loans originally included in the pool of insured obligations with an option to make a minimum payment that has the potential to negatively amortize the loan required to categorize a transaction as an Option ARM.

No definition available.

Name:	ago_MinimumPercentageOfLoansWithPotentialNegativeAmortizationForOptionArmCategory
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

Name:	ago_PeriodForApplicationOfConstantConditionalDefaultRate
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Represents the 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.

No definition available.

Name:	ago_PeriodForDefaultsFromDelinquentOrForeclosureCategory
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Represents the period until which loss severity rate would continue.

No definition available.