Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedBeyondThirtyFirstFiscalYearFromBalanceSheetDate
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 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 16 and within 20 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan16AndWithin20YearsFromBalanceSheetDate
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 21 and Within 25 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan21AndWithin25YearsFromBalanceSheetDate
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 26 and Within 30 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan26AndWithin30YearsFromBalanceSheetDate
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

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

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLosstobeExpensedDuringFiscalYearFollowingBalanceSheetDate
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 during the second quarter of the subsequent annual period following the statement of financial position reporting 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 More than 10 and within 15 Years from Balance Sheet Date

No definition available.

Name:	ago_FinancialGuaranteeInsuranceContractsFutureExpectedNetLosstobeExpensedMorethan10andwithin15YearsfromBalanceSheetDate
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.