Name:	ago_DeferredCompensationArrangementWithIndividualAwardCliffVestingPeriod
Namespace Prefix:	ago_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Represents the number of installments in which the awards are vested to officers and employees.

No definition available.

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

Represents the percentage of awards allocated to a performance period which includes the year of award and the next three years.

No definition available.

Name:	ago_DeferredCompensationArrangementWithIndividualPercentageOfAwardsAllocatedToYearOfAwardAndNextThreeYears
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the percentage of awards allocated to a performance period which includes the year of award and the next two years.

No definition available.

Name:	ago_DeferredCompensationArrangementWithIndividualPercentageOfAwardsAllocatedToYearOfAwardAndNextTwoYears
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the percentage of awards allocated to a performance period which includes the year of award and the next year.

No definition available.

Name:	ago_DeferredCompensationArrangementWithIndividualPercentageOfAwardsAllocatedToYearOfAwardAndNextYear
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the portion of awards of each installment which is increased or decreased in proportion to the increase or decrease of per share adjusted book value during the performance period.

No definition available.

Name:	ago_DeferredCompensationArrangementWithIndividualPortionOfAwardsOfEachInstallmentAdjustedInProportionToChangesInPerShareAdjustedBookValueDuringPerformancePeriod
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the portion of awards of each installment which is increased or decreased in proportion to the operating return on equity during the performance period.

No definition available.

Name:	ago_DeferredCompensationArrangementWithIndividualPortionOfAwardsOfEachInstallmentAdjustedInProportionToOperatingReturnOnEquityDuringPerformancePeriod
Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the limit on tax deductible compensation imposed by the Internal Revenue Code, with the exemption of certain types of performance-based compensation.

No definition available.

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

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 710

-SubTopic 10

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65

-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 AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 6, 7

-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 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

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

- Details

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

The minimum period that the individual is required to perform services in order to be fully vested under the deferred compensation arrangement.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-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 Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph 64, 65, A240

-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 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901