Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensed
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 beyond the twentieth year following the statement of financial position reporting date.

No definition available.

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

For financial guaranty insurance contracts, the discount amount used to arrive at the net present value of the net loss expected to be expensed over the term of the contract period.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedDiscountAmount
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 first quarter of the subsequent annual period following the statement of financial position reporting date.

No definition available.

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

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

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedDuringFiscalYearFollowingBalanceSheetDate
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 fourth quarter of the subsequent annual period following the statement of financial position reporting date.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedDuringFourthQuarterFollowingBalanceSheetDate
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_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedDuringSecondQuarterFollowingBalanceSheetDate
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 third quarter of the subsequent annual period following the statement of financial position reporting date.

No definition available.

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

For financial guaranty insurance contracts, the undiscounted amount of net loss expected to be expensed over the term of the contract period.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedFutureValue
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 fifth full fiscal year following the date of the latest balance sheet presented in the financial statements.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedInFifthFullFiscalYear
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 fourth full fiscal year following the date of the latest balance sheet presented in the financial statements.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedInFourthFullFiscalYear
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_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedInSecondFullFiscalYear
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 third full fiscal year following the date of the latest balance sheet presented in the financial statements.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedInThirdFullFiscalYear
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 during the eleventh through fifteenth year following the statement of financial position reporting date.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan10AndWithin15YearsFromBalanceSheetDate
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 during the sixteenth through twentieth year following the statement of financial position reporting date.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThan15AndWithin20YearsFromBalanceSheetDate
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 during the sixth through tenth year following the statement of financial position reporting date.

No definition available.

Name:	ago_FinancialGuarantyInsuranceContractsFutureExpectedNetLossToBeExpensedMoreThanFiveAndWithin10YearsFromBalanceSheetDate
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

For financial guaranty insurance contracts, the increase (decrease) in the amount of net loss expected to be expensed over the term of the contract period due to the effect of consolidating variable interest entities

No definition available.