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

- Details

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

Represents the cash collected against the premiums for financial guaranty insurance contracts of variable interest entity.

No definition available.

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

Amount of premium receivables under financial guarantee insurance contracts expected to be collected 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 310

-Section 50

-Paragraph 3

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of premium receivables under financial guarantee insurance contracts expected to be collected in the eleventh through the 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 310

-Section 50

-Paragraph 3

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThan10AndWithin15YearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of premium receivables under financial guarantee insurance contracts expected to be collected in the sixteenth through the 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 310

-Section 50

-Paragraph 3

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThan15AndWithin20YearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of premium receivables under financial guarantee insurance contracts expected to be collected in the sixth through the 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 310

-Section 50

-Paragraph 3

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

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

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThanFourAndWithinFiveYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThanOneAndWithinTwoYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThanThreeAndWithinFourYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumExpectedToBeCollectedMoreThanTwoAndWithinThreeYearsFromBalanceSheetDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of premium receivables under financial guarantee insurance contracts.

No definition available.