Derecognized Deferred Rent And Lease Incentive Liabilities

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

Represents the amount of payment on the termination of credit derivatives transactions which the defendant owes to plaintiff as per the calculation of plaintiff.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of payment on the termination of credit derivatives transactions which the plaintiff owes to defendant as per the calculation of defendant.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of credit derivative transactions which the entity has improperly terminated as per the allegations of the plaintiff.

+ References

No definition available.

+ Details

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Namespace Prefix:	ago_
Data Type:	xbrli:integerItemType
Balance Type:	na
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- Definition

Represents the number of credit derivative transactions which the entity has improperly calculated termination payment as per the allegations of the plaintiff.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
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- Definition

Operating Lease, Number of Square Feet

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount or range of possible amounts of gain that could be realized upon the resolution of a contingency.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

+ Details

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

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
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_LossContingenciesLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Details

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- Details

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- Details

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Commitments and Contingencies - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) ft²	Jan. 01, 2019 USD ($)	Apr. 10, 2015 USD ($) Transaction	Mar. 15, 2013 Transaction	Nov. 28, 2011 USD ($) Transaction
Commitments and Contingencies Legal Proceedings
Lease, number of square feet \| ft²	103,500
Lessee, operating lease, renewal term	5 years
Total operating lease liabilities	$ 93	$ 95
Operating Lease, Right-of-Use Asset	$ 67	69
Derecognized Deferred Rent And Lease Incentive Liabilities		$ 26
LBIE vs. AG Financial Products [Member] \| AG Financial Products Inc. [Member] \| Guarantee Obligations [Member]
Commitments and Contingencies Legal Proceedings
Number of credit derivative transactions for which termination payment is alleged to be improperly calculated \| Transaction				9	9
LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Gain contingency, number of credit derivative transactions with improperly calculated payments \| Transaction			28
Positive Outcome of Litigation [Member] \| Pending Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| AG Financial Products Inc. [Member]
Commitments and Contingencies Legal Proceedings
Termination payments which LBIE owes to AG Financial Products as per calculation of AG Financial Products					$ 29
Positive Outcome of Litigation [Member] \| Pending Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Termination payments which AG Financial Products owes to LBIE as per calculation of LBIE					$ 1,400
Minimum [Member] \| Positive Outcome of Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Gain contingency, unrecorded amount			$ 200
Maximum [Member] \| Positive Outcome of Litigation [Member] \| LBIE vs. AG Financial Products [Member] \| Lehman Brothers International (Europe) [Member]
Commitments and Contingencies Legal Proceedings
Gain contingency, unrecorded amount			$ 500