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SCHEDULE IV REINSURANCE | 12 Months Ended
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Dec. 31, 2013
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract] |
SCHEDULE IV REINSURANCE | WHITE MOUNTAINS INSURANCE GROUP, LTD. REINSURANCE (Millions)
Column A |  | Column B |  | Column C |  | Column D |  | Column E |  | Column F
Premiums earned |  | Gross amount |  | Ceded to other companies |  | Assumed from other companies |  | Net amount |  | Percentage of amount assumed to net
Years ended: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
December 31, 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
OneBeacon (1) |  | $ | 1,043.3 |  |  | $ | (71.4 | ) |  | $ | 148.5 |  |  | $ | 1,120.4 |  |  | 13.3 | %
Sirius Group |  | 174.0 |  |  | (246.2 | ) |  | 938.6 |  |  | 866.4 |  |  | 108.3 | %
December 31, 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
OneBeacon(1) |  | $ | 1,158.3 |  |  | $ | (79.1 | ) |  | $ | 52.8 |  |  | $ | 1,132.0 |  |  | 4.7 | %
Sirius Group |  | 169.9 |  |  | (226.6 | ) |  | 988.3 |  |  | 931.6 |  |  | 106.1 | %
December 31, 2011 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
OneBeacon(1) |  | $ | 1,035.9 |  |  | $ | (66.0 | ) |  | $ | 42.3 |  |  | $ | 1,012.2 |  |  | 4.2 | %
Sirius Group |  | 128.5 |  |  | (206.0 | ) |  | 989.8 |  |  | 912.3 |  |  | 108.5 | %
(1) | The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.
Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

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- Definition The entire disclosure for the supplemental schedule of reinsurance information. Reinsurance schedule includes, but is not limited to, the type of insurance, gross amount of premiums, premiums ceded to other entities, premiums assumed from other entities, net amount of premium revenue, and the percentage of the premiums assumed to net premium revenue. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 17 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17) -URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574992-122915 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.7-05.(c) Schedule IV) -URI http://asc.fasb.org/extlink&oid=6879921&loc=d3e569147-122900 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 05 -Article 7 + Details
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