Variable Interest Entity, Distributed Investments

No definition available.

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

- Definition

Variable Interest Entity, Number of Entities Consolidated

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Non-Consolidated, Number of Policies Monitored

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Number of Policies Monitored, Not Within the Scope of ASC 810

+ References

No definition available.

+ Details

Name:	ago_VariableInterestEntityNumberofPoliciesMonitoredNotWithintheScopeofASC810
Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Variable Interest Entity, Number of Policies that Contain Provisions for Consolidation

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Other Consolidated, Carrying Amount, Assets

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Other Consolidated, Carrying Amount, Liabilities

+ References

No definition available.

+ Details

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

- Definition

Variable Interest Entity, Primary Beneficiary, Custody Receipts, Notice Period

+ References

No definition available.

+ Details

Name:	ago_VariableInterestEntityPrimaryBeneficiaryCustodyReceiptsNoticePeriod
Namespace Prefix:	ago_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount classified as assets attributable to disposal group held for sale or disposed of.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 10
-SubTopic 20
-Topic 205
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483475/205-20-45-10

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-7

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5C
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-5C

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-5B

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-3

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483475/205-20-45-11

+ Details

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount after tax of gain (loss) not previously recognized resulting from the disposal of a discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5C
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-5C

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483475/205-20-45-3B

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483499/205-20-50-1

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483475/205-20-45-3

+ Details

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

- Definition

Amount classified as liabilities attributable to disposal group held for sale or disposed of.

+ References

+ Details

Name:	us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-6

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-4

+ 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 25
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481231/810-10-45-25

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (bb)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 25
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481231/810-10-45-25

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481420/860-30-50-1A

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481420/860-30-50-1A

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481420/860-30-50-1A

+ Details

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

- Definition

Amount of maximum exposure to loss from involvement with consolidated variable interest entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-5A

+ Details

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

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=ago_SoundPointAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ago_FinancialGuarantyVariableInterestEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ago_PuertoRicoTrustsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ago_StructuredFinanceAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ago_PuertoRicoTrustsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ago_ConsolidatedInvestmentVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_ArithmeticAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Additional Information (Details)	3 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) policy consolidatedInvestmentVehicle entity Entity	Jul. 01, 2024 USD ($)	Dec. 31, 2023 USD ($) consolidatedInvestmentVehicle entity Entity policy
Variable Interest Entity [Line Items]
Number of policies monitored \| policy		15,000
Number of policies monitored, not within the scope of ASC 810 \| policy		14,000
Number of policies that contain provisions for consolidation \| policy		59		68
Net fair value gains and losses on FG VIEs are expected to reverse to zero at maturity of the VIE debt		$ 485,000,000
Sound Point Agreement
Variable Interest Entity [Line Items]
Assets held for sale	$ 4,700,000,000
Deconsolidated liabilities	4,400,000,000
Loss on deconsolidation	$ 16,000,000
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Other consolidated VIE assets				$ 92,000,000
Other consolidated VIE liabilities				$ 7,000,000
Financial Guaranty Variable Interest Entities \| Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss exposure		$ 0
Financial Guaranty Variable Interest Entities \| Variable Interest Entity, Primary Beneficiary \| Puerto Rico Trusts
Variable Interest Entity [Line Items]
Total number of entities consolidated \| entity		24		24
Financial Guaranty Variable Interest Entities \| Variable Interest Entity, Primary Beneficiary \| Structured Finance and Other
Variable Interest Entity [Line Items]
Total number of entities consolidated \| Entity		23		24
Puerto Rico Trusts \| Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Custody receipts, notice period		30 days
Consolidated Investment Vehicles \| Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total number of entities consolidated \| consolidatedInvestmentVehicle		3		3
Distributed investments			$ 28,000,000
Consolidated Investment Vehicles \| Average \| Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Collateral posting requirement		$ 41,000,000		$ 41,000,000