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

The consideration due to the assuming enterprise, net of commissions as of the balance sheet date under the terms of the reinsurance contract in exchange for the right to receive reimbursement from such entity for covered claims and expenses.

No definition available.

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

Insured Financial Obligations, Ceded Par Outstanding

No definition available.

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

Represents the portion of insured risk ceded to other reinsurers.

No definition available.

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

Specialty Insurance and Reinsurance, Ceded Par Outstanding

No definition available.

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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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

Amount of funds held as security for payments to be received under reinsurance contracts.

No definition available.