Insurance Company Regulatory Requirements (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
AGC \| Maryland
Dividend Restrictions and Capital Requirements
Dividend amount available for distribution	$ 111.2
Dividend declared and paid	20.0	40.0
AGM \| New York
Dividend Restrictions and Capital Requirements
Dividend amount available for distribution	129.5
Bermuda \| AG Re
Dividend Restrictions and Capital Requirements
Dividend amount available for distribution	1,150.0
Dividend declared and paid	$ 54.0	$ 12.0
Dividend restrictions on statutory capital (as a percent)	15.00%
Relevant assets as a percentage of relevant liabilities (as a percent)	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

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

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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.

+ Details

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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.

+ Details

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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.

+ Details

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- 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

+ Details

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- 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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- 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.

+ Details

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