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

Assumed Premiums, Net of Commissions

No definition available.

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

Total expected amount of future recoveries as of the balance sheet date from reinsurers relating to ceded financial guaranty business.

No definition available.

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

Due (To) From [Abstract]

No definition available.

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

Financial Guaranty [Abstract]

No definition available.

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

Represents the amount of insured risk assumed from other insurers.

No definition available.

Name:	ago_InsuredFinancialObligationsAssumedParAmount
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

Represents the second to pay outstanding principal amounts of the underlying insured obligations for financial guaranty contracts, after netting out ceded contracts.

No definition available.

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

Non-Financial Guaranty Exposure [Abstract]

No definition available.

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

Non-Financial Guaranty Exposure, Assumed Par, Amount

No definition available.

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

Non-Financial Guaranty Exposure, Ceded Par Outstanding

No definition available.

Name:	ago_NonFinancialGuarantyExposureCededParOutstanding
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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.13(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910