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Fair Value of Financial Instruments (Details) (USD $) In Millions | Jun. 30, 2011 | Dec. 31, 2010
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior Notes | $ 669.0 | $ 818.8
WMRe Preference Shares | 250.0 | 250.0
OneBeacon U.S. Holdings, Inc. ("OBH") | Carrying Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior Notes | 269.7 | 419.6
Carrying Value | White Mountains Re. |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior Notes | 399.3 | 399.2
WMRe Preference Shares | 250.0 | 250.0
OneBeacon U.S. Holdings, Inc. ("OBH") | Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior Notes | 282.2 | 435.1
Fair Value | White Mountains Re. |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions |  |
Senior Notes | 414.7 | 390.9
WMRe Preference Shares | $ 237.5 | $ 212.5

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- Definition Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations. + 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 210.7-03.16) -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 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13,16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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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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- Definition Represents preference shares issued by a subsidiary, White Mountains Re Group Ltd. Amount is classified as equity not attributable to White Mountains (noncontrolling interest, minority interest). + Details
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