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Statutory Financial Information (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Combined statutory capital and surplus of the Insurance Subsidiaries | $ 1,063 | $ 1,100 |
Combined statutory net income of the Insurance Subsidiaries | $ 26.5 | $ 86.9 | $ 69.8
Combined total adjusted capital in excess of the authorized control level | 4.4 |  |
Montpelier U S Insurance Company [Member] |  |  |
Combined total adjusted capital in excess of the authorized control level | 7.7 |  |

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- Definition The amount of statutory adjusted capital in excess of the authorized control level risk-based capital computed using statutory accounting practices prescribed by the National Association of Insurance Commissioners. + References No definition available. + Details
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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Statement of Financial Accounting Standard (FAS) -Number 60 -Paragraph 60 -Subparagraph h -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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-Publisher AICPA -Name Statement of Position (SOP) -Number 94-5 -Paragraph 8, 9 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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- 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 + Details
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