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

For financial guaranty insurance contracts, the discount amount used to arrive at the net present value of the premiums expected to recognized over the term of the contract period.

No definition available.

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

For financial guaranty insurance contracts, the undiscounted amount of premium revenue expected to be recognized over the term of the contract period.

No definition available.

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

For financial guaranty insurance contracts, the discounted amount of premium revenue expected to be recognized over the term of the contract period.

No definition available.

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

- Details

Name:	ago_FinancialGuarantyInsurancePremiumsLineItems
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

For financial guaranty insurance contracts, the increase (decrease) in the amount of premium revenue expected to be recognized over the term of the contract period due to the effect of consolidating variable interest entities.

No definition available.

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

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the fourth fiscal quarter following the latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedDuringFourthQuarterFollowingBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the eleventh through fifteenth fiscal year following the latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 4

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedMoreThan10AndWithin15YearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the sixteenth through twentieth fiscal year following the latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 4

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedMoreThan15AndWithin20YearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the sixth through tenth fiscal year following the latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 4

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedMoreThanFiveAndWithin10YearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the fifth fiscal year following the latest fiscal year.

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedMoreThanFourAndWithinFiveYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the second fiscal year following the latest fiscal year.

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedMoreThanOneAndWithinTwoYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the fourth fiscal year following the latest fiscal year.

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedMoreThanThreeAndWithinFourYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the third fiscal year following the latest fiscal year.