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Segment Information (Assets) (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 | Dec. 31, 2012 OneBeacon | Dec. 31, 2011 OneBeacon | Dec. 31, 2012 Sirius Group | Dec. 31, 2011 Sirius Group | Dec. 31, 2012 HG Global | Dec. 31, 2011 HG Global | Dec. 31, 2012 BAM | Dec. 31, 2011 BAM | Dec. 31, 2012 Other Operations | Dec. 31, 2011 Other Operations | Dec. 31, 2012 BAM
Segment reporting information |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0
Total investments | 7,278.1 | 8,268.0 |  |  | 2,291.5 | 2,707.6 | 3,534.3 | 3,640.5 | 101.5 | 0 | 472.4 |  | 0 | 878.4 | 1,919.9 |
Reinsurance recoverable on paid and unpaid losses | 447.0 | 2,537.8 |  |  | 110.7 | 2,184.1 | 336.3 | 353.7 | 0 | 0 | 0 |  | 0 | 0 | 0 |
Assets held for sale | 2,226.8 | 132.6 |  |  | 2,226.8 | 132.6 | 0 | 0 | 0 | 0 | 0 |  | 0 | 0 | 0 |
Assets | 12,895.4 | 14,064.0 |  |  | 5,382.3 | 5,792.4 | 5,962.0 | 5,337.9 | 623.6 | 0 | (28.6) | [1] | 0 | 956.1 | 2,933.7 |
Loss and loss adjustment expense reserves | 3,168.9 | 5,702.3 | 5,736.8 | 6,379.2 | 1,000.0 | 3,358.6 | 2,168.9 | 2,343.7 | 0 | 0 | 0 |  | 0 | 0 | 0 |
Liabilities held for sale | 2,226.8 | 107.6 |  |  | 2,226.8 | 107.6 | 0 | 0 | 0 | 0 | 0 |  | 0 | 0 | 0 |
Liabilities | 8,637.2 | 9,396.1 |  |  | 4,365.0 | 4,678.5 | 4,123.2 | 3,784.1 | 0.9 | 0 | 7.4 |  | 0 | 140.7 | 933.5 |
Non-controlling interest | 526.4 | 580.2 |  |  | 254.2 | 287.2 | 279.1 | 289.5 | 16.5 | 0 | (36.0) |  | 0 | 12.6 | 3.5 |
Total White Mountains’ common shareholders’ equity | 3,731.8 | 4,087.7 |  |  | 763.1 | 826.7 | 1,559.7 | 1,264.3 | 606.2 | 0 | 0 |  | 0 | 802.8 | 1,996.7 |
Interest income (expense), surplus notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0
[1] | BAM total assets reflect the elimination of $503.0 in surplus notes issued to HG Global and its subsidiaries, and $18.4 in accrued interest related to those surplus notes.

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