Represents the discount rate used to calculate present value for surveillance purposes.

No definition available.

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- Definition

The maximum amount of statutory capital that may be paid out as dividends without prior approval from a regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Amount of dividends declared in the current accounting period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

The maximum percentage of statutory capital that may be paid out as dividends without prior approval from a regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

The maximum percentage of statutory capital and surplus that may be paid out as dividends without prior approval from a regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

Represents the period prior to dividend payment by which the entity is required to file an affidavit stating that it will continue to meet required margins, in order to make dividend payments more than the prescribed percentage.

+ References

No definition available.

+ Details

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Data Type:	us-types:durationStringItemType
Balance Type:	na
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- Definition

Represents the maximum dividends allowed by the purchase agreement on the acquiree's equity interests for a specified period following the date of acquisition, expressed as a percentage of the debt service requirements of the acquiree.

+ References

No definition available.

+ Details

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Namespace Prefix:	ago_
Data Type:	num:percentItemType
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Period Type:	instant

- Details

Name:	ago_RegulatoryAmountAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage applied to cumulative earned premiums to determine the contingency reserve for all policies written prior to July 1, 1989.

+ References

No definition available.

+ Details

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Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage applied to premiums written for each category of insured obligation to determine the contingency reserve for all policies written on or after July 1, 1989.

+ References

No definition available.

+ Details

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Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the portion of the required contingency reserve for each category of insured obligation that is provided per quarter.

+ References

No definition available.

+ Details

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Namespace Prefix:	ago_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the period from the balance sheet date within which deferred tax assets must be expected to be realized to be admitted for statutory accounting purposes as prescribed or permitted by state laws and regulations.

+ References

No definition available.

+ Details

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Data Type:	us-types:durationStringItemType
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- Definition

Represents the minimum relevant assets required to be maintained under prescribed or permitted statutory accounting practices, expressed as a percentage of relevant liabilities.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of dividends that may be paid or declared in any calendar year without prior approval of regulatory agencies.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 08

-Paragraph e

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(e))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of dividends distributed to shareholders in the current accounting period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 60

-Subparagraph h(3)

-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 Accounting Standards Codification

-Topic 944

-SubTopic 50

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6483535&loc=d3e16392-158451

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Balance Type:	debit
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Balance Type:	na
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- Definition

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.23(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 60

-Subparagraph h

-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 AICPA

-Name Statement of Position (SOP)

-Number 94-5

-Paragraph 8, 9

-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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 24

-Subparagraph c

+ Details

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

- Definition

Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 24

-Subparagraph c

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.23(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

- Definition

Financial instruments issued by insurance entities (surplus notes) that are includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations that are liabilities of the issuer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 470

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6486086&loc=d3e24387-158525

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Insurance Company Regulatory Requirements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Insurance company regulatory requirements
Percentage of cumulative earned premiums used to determine contingency reserve for all policies written prior to July 1, 1989	50.00%
Percentage of premiums written used to determine contingency reserve for all policies written on or after July 1, 1989	50.00%
Period within which deferred tax assets must be expected to be realized to be permitted (in years)	1 year
Rate at which present value of expected losses are discounted (as a percent)	5.00%
Minimum
Insurance company regulatory requirements
Amounts provided each quarter, of the total required for each category, less permitted reductions	1.25%
Maximum
Insurance company regulatory requirements
Amounts provided each quarter, of the total required for each category, less permitted reductions	1.6667%
AG Re
Insurance Regulatory Amounts Reported
Policyholder's surplus	$ 1,290.6	$ 1,190.4
Net Income (Loss)	141.2	(26.4)	8.5
AGC
Insurance Regulatory Amounts Reported
Policyholder's surplus	1,021.5	854.1
Net Income (Loss)	229.9	(182.1)	(243.1)
Surplus note issued			300.0
AGM
Insurance Regulatory Amounts Reported
Policyholder's surplus	1,227.2	992.7
Net Income (Loss)	632.2	401.8	(228.2)
AGMH
Insurance Regulatory Amounts Reported
Maximum dividends allowed under purchase agreement, expressed as a percentage of debt service requirements	125.00%
Maryland \| AGC
Insurance Regulatory Amounts Reported
Amount available for distribution	102.1
Dividends paid	30.0	50.0	16.8
New York \| AGM
Insurance Regulatory Amounts Reported
Amount available for distribution	120.9
Bermuda \| AG Re
Insurance Regulatory Amounts Reported
Amount available for distribution	845.0
Dividends paid	86.0	24.0	30.3
Dividend restrictions on statutory capital (as a percent)	15.00%
Dividend restrictions on statutory capital	193.6
Relevant assets as a percentage of relevant liabilities	75.00%
Dividend restrictions on statutory capital and surplus (as a percent)	25.00%
Period for filing affidavit prior to dividend payment (in days)	7 days
Dividend declared			$ 26.6