Name:	ago_CreditDerivativeBankProfit
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the bank profit expressed as a percentage of original or gross spread.

No definition available.

Name:	ago_CreditDerivativeBankProfitAsPercentageOfOriginalGrossSpreadOrCashBondPrice
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the gross spread allocated to hedge cost. Hedge cost represents the cost of protection purchased on the entity by the originator to hedge their counterparty credit risk exposure to the entity.

No definition available.

Name:	ago_CreditDerivativeHedgeCost
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the hedge cost expressed as a percentage of original or gross spread.

No definition available.

Name:	ago_CreditDerivativeHedgeCostAsPercentageOfOriginalGrossSpreadOrCashBondPrice
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the number of sources on which credit spread is based.

No definition available.

Name:	ago_CreditDerivativeNumberOfSourcesOfCreditSpread
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the original gross spread/cash bond price. Gross spread is the difference between the yield of a security paid by an issuer on an insured versus uninsured basis or in the case of a CDS transaction the difference between the yield and an index such as LIBOR.

No definition available.

Name:	ago_CreditDerivativeOriginalGrossSpreadOrCashBondPrice
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the percentage of gross spread.

No definition available.

Name:	ago_CreditDerivativeOriginalGrossSpreadPercentage
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the percentage of exposure hedged by the bank or deal originator.

No definition available.

Name:	ago_CreditDerivativePercentageOfExposureHedgedByOriginator
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the gross spread allocated to net spread. It represents the premiums received by the company for the credit protection provided. Such net spread varies based on the variation in the gross spread, bank profit and hedged cost.

No definition available.

Name:	ago_CreditDerivativePremiumReceivedPerAnnum
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the premiums received per annum by the company expressed as a percentage of original or gross spread.

No definition available.

Name:	ago_CreditDerivativePremiumReceivedPerAnnumAsPercentageOfOriginalGrossSpreadOrCashBondPrice
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the percentage of fixed maturity securities which have been valued using model processes set by the entity to the company's fixed-income securities and short-term investments which are valued at fair value.

No definition available.

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

Represents the number of fixed maturity securities which have been valued using model processes set by the entity.

No definition available.

Name:	ago_NumberOfFixedMaturitySecuritiesValuedUsingModelProcesses
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

This element represents the fair value investments categorized as other which are not in and of themselves material enough to require separate disclosure.

No definition available.

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

Represents the percentage of CDS contracts which are fair valued using minimum premium. Minimum premium is the minimum rate that the company would currently charge to assume similar risks.

No definition available.

Name:	ago_PercentageOfCdsContractsFairValuedUsingMinimumPremium
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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

- Details

Name:	us-gaap_CreditDerivativesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258