Claims Paid, Net

No definition available.

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- Definition

Represents the outstanding principal amounts of the underlying insured obligations for financial guaranty contracts accounted for as insurance, net of ceded contracts.

+ References

No definition available.

+ Details

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

- Definition

Represents the outstanding principal amounts of the underlying insured obligations for financial guaranty contracts accounted for as insurance.

+ References

No definition available.

+ Details

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

- Definition

Represents the net outstanding principal amounts of the underlying insured obligations for financial guaranty contracts accounted for as insurance.

+ References

No definition available.

+ Details

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

- Definition

Increase Decrease in Projected Expected Loss to be Paid

+ References

No definition available.

+ Details

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

- Definition

Total amount of cumulative payments made to date to settle insured claims and pay costs incurred in the claims settlement process.

+ References

No definition available.

+ Details

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

- Definition

Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims, for the largest loss on a single insured transaction.

+ References

No definition available.

+ Details

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

- Definition

Number of Assumed Transactions With Expected Losses to be Paid

+ References

No definition available.

+ Details

Name:	ago_NumberOfAssumedTransactionsWithExpectedLossesToBePaid
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Direct Transactions With Expected Losses to be Paid

+ References

No definition available.

+ Details

Name:	ago_NumberOfDirectTransactionsWithExpectedLossesToBePaid
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of transactions insured by the entity.

+ References

No definition available.

+ Details

Name:	ago_NumberOfTransactionsInsured
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the entity's estimate of the present value of future claim payments, net of reinsurance and net of salvage and subrogation which includes the present value benefit of estimated recoveries for breaches of R&W, including the effect of consolidating VIEs and excluding loss adjustment expenses.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

This item represents a non-contingent liability for the fair value of an obligation to stand ready to perform over the term of a guaranty issued in the event that specified triggering events or conditions occur.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 25

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7661617&loc=d3e11019-110243

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 5, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.15)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 3

-Subparagraph b, d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 25

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=7661617&loc=d3e11049-110243

+ Details

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

- Definition

Alternate concept name for the aggregate amount of policy reserves (provided for future obligations including unpaid claims and claims adjustment expenses) and policy benefits (liability for future policy benefits) as of the balance sheet date; grouped amount of all the liabilities associated with the company's insurance policies.

+ References

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 94-5

-Paragraph 11

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.13(a)(1))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Subparagraph a

-Article 7

+ Details

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

Financial Guaranty Insurance Contracts (Details 10) In Millions, unless otherwise specified						3 Months Ended																					3 Months Ended
	Sep. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2012 Life Insurance [Member] Below investment grade (BIG) USD ($)	Sep. 30, 2012 Life Insurance [Member] Below investment grade (BIG) Ballantyne Re Plc and Orkney Re II Plc [Member] Transaction	Sep. 30, 2012 Student Loan [Member] USD ($)	Sep. 30, 2012 Trust Preferred Securities Collateralized Debt Obligations [Member] USD ($)	Sep. 30, 2012 Trust Preferred Securities Collateralized Debt Obligations [Member] Below investment grade (BIG) USD ($)	Sep. 30, 2012 Public Finance Student Loan [Member] USD ($)	Sep. 30, 2012 Public Finance Student Loan [Member] Below investment grade (BIG) USD ($)	Sep. 30, 2012 Asset-backed Student Loan [Member] USD ($)	Sep. 30, 2012 Asset-backed Student Loan [Member] Below investment grade (BIG) USD ($)	Sep. 30, 2012 Public Finance Jefferson County Alabama Sewer Authority [Member] USD ($)	Sep. 30, 2012 Public Finance City of Stockton Pension Obligation and Lease Revenue Bonds [Member] [Member] USD ($)	Sep. 30, 2012 Manufactured Housing Loans [Member] USD ($)	Jun. 30, 2012 Manufactured Housing Loans [Member] USD ($)	Dec. 31, 2011 Manufactured Housing Loans [Member] Transaction	Sep. 30, 2012 Manufactured Housing Loans [Member] Below investment grade (BIG) USD ($)	Sep. 30, 2012 Public Finance Harrisburg Pennsylvania [Member] USD ($)	Sep. 30, 2012 Public Finance Harrisburg Pennsylvania [Member] Below investment grade (BIG) USD ($)	Sep. 30, 2012 Public Finance bonds secured by excess free cash flows of Foxwoods Casino [Member] USD ($)	Jun. 30, 2012 Sovereign Debt [Member] USD ($)	Jun. 30, 2012 Sovereign Debt [Member] EUR (€)	Sep. 30, 2012 Public Finance Jefferson County Alabama Sewer Authority Bonds [Member] USD ($)	Sep. 30, 2012 Public Finance Jefferson County Alabama Sewer Authority Warrants [Member] USD ($)	Sep. 30, 2012 Troubled Municipal Credits [Member] USD ($)	Jun. 30, 2012 Troubled Municipal Credits [Member] USD ($)	Sep. 30, 2012 Spanish sub-sovereign debt [Member] USD ($)	Sep. 30, 2012 Public Finance Luoisville Arena Authority [Member] USD ($)
Financial guarantee obligations
Claims Paid, Net													$ 8								$ 289
Exposure of Debt																						314					444
Net Exposure of Debt												708	160									218					319	336
Net Par Outstanding Financial Guaranty Insurance			2,300		2,600	1,600	725	1,300	445	1,300	150	479		306			210						206	273
Guaranty Liabilities																								32
Gross Expected Loss	594	679	883		7													156	95	26
Number of transactions insured				2
Largest Expected Loss to be Paid for a Single Transaction					25	9								31	26
Number of Direct Transactions With Expected Losses to be Paid																2
Number of Assumed Transactions With Expected Losses to be Paid																1
Projected Net Expected Loss			134		56							197													10	58	34
Increase (Decrease) in Projected Expected Loss to be Paid						2																					31
Net Claims to Date																		$ 10		$ 86