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

Financial Guarantee Insurance Contracts Future Expected Net Loss to be Expensed During Fourth Quarter Following Balance Sheet Date

No definition available.

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

Financial Guarantee Insurance Contracts, Future Expected, Net Loss to be Expensed During Remainder of Fiscal Year Following Balance Sheet Date

No definition available.

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

Financial Guarantee Insurance Contracts, Future Expected, Net Loss to be Expensed During Second Quarter Following Balance Sheet Date

No definition available.

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

Financial Guarantee Insurance Contracts Future Expected Net Loss to be Expensed During Third Quarter Following Balance Sheet Date

No definition available.

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

Financial Guarantee Insurance Contracts, Future Expected, Net Loss to be Expensed in First Full Fiscal Year

No definition available.

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

Financial Guarantee Insurance Contracts Future Expected Net Loss to be Expensed More than 14 and Within 19 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan14AndWithin19YearsFromBalanceSheetDate
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financial Guarantee Insurance Contracts Future Expected Net Loss to be Expensed More than 9 and Within 14 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan9AndWithin14YearsFromBalanceSheetDate
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financial Guarantee Insurance Contracts Future Expected Net Loss to be Expensed More than Four and Within 9 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThanFourAndWithin9YearsFromBalanceSheetDate
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

For financial guarantee insurance contracts, the amount of net loss expected to be expensed within the fourth full fiscal year following the date of the latest balance sheet presented in the financial statements.

No definition available.

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

For financial guaranty insurance contracts, the amount of net loss expected to be expensed within the second full fiscal year following the date of the latest balance sheet presented in the financial statements.

No definition available.

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

Financial Guarantee Insurance Contracts, Future Expected, Net Loss to be Expensed in Third Full Fiscal Year

No definition available.

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

Financial Guarantee Insurance Contracts, Net Loss to be Expensed, Present Value

No definition available.

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

Financial Guarantee Insurance Contracts, Net Loss to be Expensed, Undiscounted

No definition available.

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

Schedule of Insured Financial Obligations with Credit Deterioration, Reductions of Gross Claim Liability, Net of Reinsurance Recoverable, Discount (Accretion)

No definition available.

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

- References

No definition available.