Discontinued Operation, Continuing Involvement, Investment Management Commitment

No definition available.

Name:	ago_DiscontinuedOperationContinuingInvolvementInvestmentManagementCommitment
Namespace Prefix:	ago_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Disposal Group, Including Discontinued Operation, Consideration, Equity Interest, Ownership Percentage

+ References

No definition available.

+ Details

Name:	ago_DisposalGroupIncludingDiscontinuedOperationConsiderationEquityInterestOwnershipPercentage
Namespace Prefix:	ago_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Holding Companies with Outstanding Public Debt, Number

+ References

No definition available.

+ Details

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

- Definition

Amount of operating expense attributable to disposal group, including, but not limited to, discontinued operation.

+ References

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

+ Details

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Business and Basis of Presentation - Narrative (Details) $ in Millions		3 Months Ended	6 Months Ended
	Jul. 01, 2023 USD ($)	Jun. 30, 2023 USD ($) Company	Jun. 30, 2023 USD ($) Company
Long-Lived Assets Held-for-sale [Line Items]
Number of holding companies with outstanding public debt \| Company		2	2
Disposal Group, Held-for-sale, Not Discontinued Operations \| Sound Point Agreement
Long-Lived Assets Held-for-sale [Line Items]
Expenses recognized		$ 24	$ 31
Subsequent Event \| Disposal Group, Held-for-sale, Not Discontinued Operations \| Sound Point Agreement
Long-Lived Assets Held-for-sale [Line Items]
Transaction commitment, new and transitioned investments	$ 1,000
Participation percentage	30.00%