Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenuetobeRecognizedBeyondYear20
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Fiscal Year

No definition available.

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

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

No definition available.

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

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

No definition available.

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

Amount of unearned premium revenue in the statement of financial position for financial guaranty insurance contracts, net of the unexpired portion of premiums ceded and before adjustment for loss claims paid but not yet expensed.

No definition available.

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

- Details

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

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the next fiscal quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedDuringFirstQuarterFollowingBalanceSheetDate
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 quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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 second fiscal quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedDuringSecondQuarterFollowingBalanceSheetDate
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 quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

Name:	us-gaap_FinancialGuaranteeInsuranceContractsFutureExpectedPremiumRevenueToBeRecognizedDuringThirdQuarterFollowingBalanceSheetDate
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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.