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

The maximum percentage of statutory capital that may be paid out as dividends without prior approval from a regulatory agency.

No definition available.

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

The maximum percentage of statutory capital and surplus that may be paid out as dividends without prior approval from a regulatory agency.

No definition available.

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

Represents the period prior to dividend payment by which the entity is required to file an affidavit stating that it will continue to meet required margins, in order to make dividend payments more than the prescribed percentage.

No definition available.

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

Dividend Payments Restrictions Schedule, Statutory Surplus

No definition available.

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

Statutory Accounting Practices, Contingency Reserves Reassumed

No definition available.

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

Statutory Accounting Practices, Contingency Reserves Reassumed, Release of Assets

No definition available.

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

Statutory Accounting Practices, Contingency Reserves Reassumed, Remainder of Fiscal Year, Amount

No definition available.

Name:	ago_StatutoryAccountingPracticesContingencyReservesReassumedRemainderofFiscalYearAmount
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Statutory Accounting Practices, Contingency Reserves Reassumed, Remainder of Fiscal Year, Percentage

No definition available.

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

Statutory Accounting Practices, Contingency Reserves Reassumed, Year Three, Percentage

No definition available.

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

Statutory Accounting Practices, Contingency Reserves Reassumed, Year Two, Percentage

No definition available.

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

Statutory Accounting Practices, Contingency Reserves, Release of Assets

No definition available.

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

Statutory Accounting Practices, Excess Capital and Surplus

No definition available.

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

Statutory Accounting Practices, Reassumed Contingency Reserves

No definition available.

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

Represents the minimum relevant assets required to be maintained under prescribed or permitted statutory accounting practices, expressed as a percentage of relevant liabilities.

No definition available.

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

Statutory Accounting Practices, Statutory Threshold for Dividend Payments, Percentage of Adjusted Net Investment Income

No definition available.

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

Statutory Accounting Practices, Statutory Threshold for Dividend Payments, Percentage of Policyholder' Surplus

No definition available.

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

Unencumbered Assets which are not held in truast for the benefit of cedants.

No definition available.

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

Amount of statutory capital and surplus computed using prescribed or permitted statutory accounting practice.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

Name:	us-gaap_DividendPaymentsRestrictionsScheduleStatutoryCapitalAndSurplus1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The cash inflow from a long-term borrowing made from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth. Alternate caption: Proceeds from Advances from Affiliates.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

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

The cash outflow for the payment of a long-term borrowing made from a related party where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth. Alternate caption: Payments for Advances from Affiliates.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Name:	us-gaap_RepaymentsOfRelatedPartyDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of dividends paid subject to regulatory approval.

No definition available.