-- None. No documentation exists for this element. --

No definition available.

Name:	ago_CreditRiskDerivativesAtFairValueBeforeEffectOfCreditSpreadNet1Abstract
Namespace Prefix:	ago_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair Value, Option, Changes in Fair Value, Gain (Loss) on Acceleration of Lien

+ References

No definition available.

+ Details

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

- Definition

Fair Value, Option, Liabilities with Recourse, Unpaid Principal Balance

+ References

No definition available.

+ Details

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

- Definition

Fair Value, Option, Loans Held as Liabilities, 90 Days or More Past Due, Aggregate Difference

+ References

No definition available.

+ Details

Name:	ago_FairValueOptionLoansHeldasLiabilities90DaysorMorePastDueAggregateDifference
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of the variable interest entity's revenues consolidated into the statement of income, including interest income, net realized and unrealized gains (losses) on assets, and other income, net of the amount of the variable interest entity's expenses consolidated into the statement of income, including interest expense, net realized and unrealized gains (losses) on liabilities with and without recourse, and other expenses.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of variable interest entities for which debt was fully paid off during the period.

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Number of Entities

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Number of Entities to be Deconsolidated

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Reporting Entity Involvement, Trustee Report General Preparation Threshold

+ References

No definition available.

+ Details

Name:	ago_VariableInterestEntityReportingEntityInvolvementTrusteeReportGeneralPreparationThreshold
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the gain (loss) recognized by the parent and included in its attributable portion of net income for the period due to deconsolidation of a subsidiary or derecognition of a group of assets. The gain (loss) recognized and included in the net income attributable to the parent for the period is generally computed as the difference between: (a) the aggregate of: (1) the fair value of any consideration received; (2) the fair value of any retained noncontrolling investment in the former subsidiary at the date the subsidiary was deconsolidated; and (3) the carrying amount of any noncontrolling interest in the former subsidiary (including any accumulated other comprehensive income attributable to the noncontrolling interest) at the date the subsidiary was deconsolidated and (b) the carrying amount of the former subsidiary's assets and liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=64809438&loc=SL4582445-111684

+ Details

Name:	us-gaap_DeconsolidationGainOrLossAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the estimated amount of gains or losses included in earnings during the period attributable to changes in instrument-specific credit risk arising from loans and other receivables held as assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

+ Details

Name:	us-gaap_FairValueOptionCreditRiskGainsLossesOnAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateDifference
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5747-111685

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryAggregatedDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityNotPrimaryBeneficiaryAggregatedDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ago_ResidentialMortgageBackedSecuritiesandOtherInsuranceProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Consolidated Variable Interest Entities - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) Entity	Dec. 31, 2015 USD ($) Entity	Dec. 31, 2014 USD ($) Entity	Dec. 31, 2013 Entity
Variable Interest Entity [Line Items]
Net fair value gains and losses on FG VIEs are expected to reverse to zero at maturity of the VIE debt	$ 0
Trustee report general preparation period	30 days
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Fair value gains (losses) on financial guaranty variable interest entities	$ 38,000,000	$ 38,000,000	$ 255,000,000
Number of entities to be deconsolidated \| Entity			7
Number of FG VIE's matured \| Entity			2
Variable Interest Entity, Primary Beneficiary [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Fair value gains (losses) on financial guaranty variable interest entities	$ 38,000,000	$ 38,000,000	$ 255,000,000
Net gain on deconsolidation			120,000,000
Gain from Company's exercise of options			$ 37,000,000
Number of FG VIE's matured \| Entity	1	2	2
Number of VIE that did not require consolidation \| Entity	32	34	32	40
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Number of VIE that did not require consolidation \| Entity	600	750
Residential Mortgage Backed Securities and Other Insurance Products [Member] \| Variable Interest Entity, Primary Beneficiary [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Total unpaid principal balance for the VIEs' assets that were over 90 days or more past due	$ 137,000,000	$ 154,000,000
Difference between the aggregate unpaid principal and aggregate fair value of the VIEs' Assets	432,000,000	804,000,000
Change in the instrument specific credit risk of the VIEs' assets	55,000,000	90,000,000	$ 116,000,000
Unpaid principal for FG VIEs’ liabilities with recourse	871,000,000	1,436,000,000
Unpaid principal for FG VIEs' liabilities with and without recourse	$ 109,000,000	$ 423,000,000