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

- Details

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

Liability for Unpaid Claims and Claims Adjustment Expense, Net of Reinsurance and Salvage, Subrogation and Other Recoveries

No definition available.

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

Liability for Unpaid Claims and Claims Adjustment Expense, Other Recoverable

No definition available.

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

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

No definition available.

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

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.

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

Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims.

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)

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

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

-Publisher SEC

-Name Financial Reporting Release (FRR)

-Number 403

-Paragraph 04

-Subparagraph b

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Subparagraph a

-Article 7

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

Amount after valuation allowance recoverable under reinsurance contracts for claims and claims adjustments.

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

The estimated amount as of the balance sheet date to be received by an insurer from the sale of property (usually damaged) on which the insurer has paid a total claim to the insured and has obtained title to the property and the right of an insurer to pursue any course of recovery of damages, in its name or in the name of the policyholder, against a third party who is liable for costs relating to an insured event that have been paid by the insurer. Estimated salvage and subrogation is generally deducted from the liability for unpaid claims.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 30

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6482241&loc=d3e13779-158432

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 30

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6482241&loc=d3e13783-158432