Name:	ago_ConditionalDefaultRateIntermediateStressPeriod
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
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:	xbrli:durationItemType
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

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:	xbrli:durationItemType
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:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Period Company Reduced Base Scenario

No definition available.

Name:	ago_PeriodCompanyReducedBaseScenario
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Period Company Reduced Most Optimistic Case for Market Recovery

No definition available.

Name:	ago_PeriodCompanyReducedMostOptimisticCaseForMarketRecovery
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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:	xbrli:durationItemType
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:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the period until which loss severity rate would continue.

No definition available.