Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedAccretiononNetEarnedPremium
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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_FinancialGuaranteeInsuranceContractsFutureExpectedNetEarnedPremiumtobeRecognized
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Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Fiscal Year

No definition available.

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Namespace Prefix:	ago_
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For financial guarantee insurance contracts, the amount of premium revenue expected to be recognized beyond the twentieth year following the statement of financial position reporting date.

No definition available.

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Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
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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.

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

[Line Items] for Financial Guarantee Insurance Premiums [Table]

No definition available.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of premium revenue under financial guarantee insurance contract to be recognized in fourth fiscal quarter following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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Amount of premium revenue under financial guarantee insurance contract to be recognized in third fiscal quarter following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of premium revenue under financial guarantee insurance contract to be recognized in eleventh through fifteenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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Period Type:	instant

Amount of premium revenue under financial guarantee insurance contract to be recognized in sixteenth through twentieth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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Amount of premium revenue under financial guarantee insurance contract to be recognized in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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Amount of premium revenue under financial guarantee insurance contract to be recognized in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Period Type:	instant

Amount of premium revenue under financial guarantee insurance contract to be recognized in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of premium revenue under financial guarantee insurance contract to be recognized in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Namespace Prefix:	us-gaap_
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Amount of premium revenue under financial guarantee insurance contract to be recognized in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).