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Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2012 | Dec. 31, 2011
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior notes | $ 677.2 | $ 677.5
SIG Preference Shares | 250.0 | 250.0
OBH Senior Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior notes | 269.8 | 269.8
Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
SIG Preference Shares | 240.0 | 217.5
Fair Value | OBH Senior Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior notes | 277.7 | 277.4
Fair Value | SIG Senior Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior notes | 417.8 | 418.6
Carrying Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
SIG Preference Shares | 250.0 | 250.0
Carrying Value | OBH Senior Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior notes | 269.8 | 269.8
Carrying Value | SIG Senior Notes |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior notes | $ 399.3 | $ 399.3

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- Definition Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 7 -Section 03 -Paragraph 16 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 + Details
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- Definition Represents preference shares issued by a subsidiary, Sirius Group Ltd. Amount is classified as equity not attributable to White Mountains (noncontrolling interest, minority interest). + References No definition available. + Details
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