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Represents the number of holding companies in the entity's organizational structure having outstanding public debt.

No definition available.

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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.

No definition available.

Name:	us-gaap_BusinessAcquisitionLineItems
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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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-Publisher FASB
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-Topic 805
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Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
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Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

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- References

No definition available.

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The cash outflow associated with other payments to acquire businesses including deposit on pending acquisitions and preacquisition costs.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
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Data Type:	na
Balance Type:
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Name:	us-gaap_BusinessAcquisitionAxis=ago_BlueMountainAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
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