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

Effective Income Tax Rate Reconciliation, Value Added Tax Rate, Percent

No definition available.

Name:	ago_EffectiveIncomeTaxRateReconciliationValueAddedTaxRatePercent
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

Represents the liability as of the balance sheet date under the tax allocation agreement.

No definition available.

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

Represents the amount of reduction in the liability under the tax allocation agreement due to payments made during the period.

No definition available.

Name:	ago_ReductionInLiabilityForTaxBasisStepUpAdjustment
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Carryforwards

-URI http://asc.fasb.org/extlink&oid=6506874

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

Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

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

Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

Name:	us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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

Name:	dei_LegalEntityAxis=ago_AssuredGuarantyReOverseasLtd.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_IncomeTaxAuthorityAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatutoryAccountingPracticesByJurisdictionAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_TaxCreditCarryforwardAxis=ago_AlternativeMinimumTaxCreditCarryforwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_TaxPeriodAxis=ago_April12014toApril12015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: