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

FInancial Guaranty Insurance Other Recoveries

No definition available.

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

The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims incurred by the ceding insurer and associated claims settlement expenses, including estimated amounts for claims incurred but not reported, and policy benefits, net of any related valuation allowance.

No definition available.

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

Represents the effect on the aggregate amount of policy reserves (provided for future obligations including unpaid claims and claims adjustment expenses) and policy benefits (liability for future policy benefits), from breached representations and warranties.

No definition available.

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

No definition available.

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

No definition available.

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

Represents the reserve for losses and loss adjustment expenses, net of reinsurance recoverable on unpaid losses and net of salvage and subrogation recoverable.

No definition available.

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

Represents the aggregate amount of policy reserves (provided for future obligations including unpaid claims and claims adjustment expenses) and policy benefits (liability for future policy benefits) as of the balance sheet date; grouped amount of all the liabilities associated with the company's net of reinsurance policies.

No definition available.

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

Reserve for Losses and Loss Adjustment Expenses Net of Reinsurance Recoverable and Salvage and Subrogation Recoverable Payable

No definition available.

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

Reserve for Losses and Loss Adjustment Expenses, Net of Reinsurance, Salvage and Subrogation and Other Recoveries

No definition available.

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

Reserve for Losses and Loss Adjustment Expenses, Other Nonfinancial Guaranty Business

No definition available.

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

Represents the net of assets and liability value when the expected salvage and subrogation exceeds the estimated loss reserve for a policy, for ceded contracts.

No definition available.

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

Represents the effect on the salvage and subrogation recoverable of breached representations and warranties.

No definition available.

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

Represents the effect on the salvage and subrogation recoverable of breached representations and warranties related to consolidating VIEs.

No definition available.

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

Represents the effect on the salvage and subrogation recoverable of breached representations and warranties after adjustments for consolidating VIEs.

No definition available.

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

The asset value when the expected salvage and subrogation exceeds the estimated loss reserve for a policy.

No definition available.

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

- Details

Name:	us-gaap_GuaranteeObligationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (a),(b),(c)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437