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Third Party Reinsurance (Tables) | 12 Months Ended
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Dec. 31, 2012
Reinsurance Disclosures [Abstract] |
Schedule of direct assumed and ceded amounts | The effects of reinsurance on White Mountains’ insurance and reinsurance subsidiaries’ written and earned premiums and on losses and LAE were as follows:
|  | Year ended December 31, 2012
Millions |  | OneBeacon |  | Sirius Group |  | Total
Written premiums: |  |  |  |  |  |
Direct |  | $ | 1,204.0 |  |  | $ | 186.1 |  |  | $ | 1,390.1 |
Assumed |  | 55.2 |  |  | 992.7 |  |  | 1,047.9 |
Gross written premiums |  | 1,259.2 |  |  | 1,178.8 |  |  | 2,438.0 |
Ceded |  | (80.0 | ) |  | (231.1 | ) |  | (311.1 | )
Net written premiums |  | $ | 1,179.2 |  |  | $ | 947.7 |  |  | $ | 2,126.9 |
Earned premiums: |  |  |  |  |  |
Direct |  | $ | 1,158.3 |  |  | $ | 169.9 |  |  | $ | 1,328.2 |
Assumed |  | 52.8 |  |  | 988.3 |  |  | 1,041.1 |
Gross earned premiums |  | 1,211.1 |  |  | 1,158.2 |  |  | 2,369.3 |
Ceded |  | (79.1 | ) |  | (226.6 | ) |  | (305.7 | )
Net earned premiums |  | $ | 1,132.0 |  |  | $ | 931.6 |  |  | $ | 2,063.6 |
Losses and LAE: |  |  |  |  |  |
Direct |  | $ | 687.5 |  |  | $ | 96.9 |  |  | $ | 784.4 |
Assumed |  | 29.6 |  |  | 523.9 |  |  | 553.5 |
Gross losses and LAE |  | 717.1 |  |  | 620.8 |  |  | 1,337.9 |
Ceded |  | (67.1 | ) |  | (76.9 | ) |  | (144.0 | )
Net losses and LAE |  | $ | 650.0 |  |  | $ | 543.9 |  |  | $ | 1,193.9 |
|  | Year ended December 31, 2011
Millions |  | OneBeacon |  | Sirius Group |  | Total
Written premiums: |  |  |  |  |  |
Direct |  | $ | 1,079.2 |  |  | $ | 139.5 |  |  | $ | 1,218.7 |
Assumed |  | 49.1 |  |  | 988.6 |  |  | 1,037.7 |
Gross written premiums |  | 1,128.3 |  |  | 1,128.1 |  |  | 2,256.4 |
Ceded |  | (65.6 | ) |  | (212.4 | ) |  | (278.0 | )
Net written premiums |  | $ | 1,062.7 |  |  | $ | 915.7 |  |  | $ | 1,978.4 |
Earned premiums: |  |  |  |  |  |
Direct |  | $ | 1,035.9 |  |  | $ | 128.5 |  |  | $ | 1,164.4 |
Assumed |  | 42.3 |  |  | 989.8 |  |  | 1,032.1 |
Gross earned premiums |  | 1,078.2 |  |  | 1,118.3 |  |  | 2,196.5 |
Ceded |  | (66.0 | ) |  | (206.0 | ) |  | (272.0 | )
Net earned premiums |  | $ | 1,012.2 |  |  | $ | 912.3 |  |  | $ | 1,924.5 |
Losses and LAE: |  |  |  |  |  |
Direct |  | $ | 551.8 |  |  | $ | 80.0 |  |  | $ | 631.8 |
Assumed |  | 9.2 |  |  | 627.8 |  |  | 637.0 |
Gross losses and LAE |  | 561.0 |  |  | 707.8 |  |  | 1,268.8 |
Ceded |  | (12.7 | ) |  | (81.8 | ) |  | (94.5 | )
Net losses and LAE |  | $ | 548.3 |  |  | $ | 626.0 |  |  | $ | 1,174.3 |
|  | Year ended December 31, 2010
Millions |  | OneBeacon |  | Sirius Group |  | Total
Written premiums: |  |  |  |  |  |
Direct |  | $ | 1,236.7 |  |  | $ | 121.6 |  |  | $ | 1,358.3 |
Assumed |  | 55.8 |  |  | 957.5 |  |  | 1,013.3 |
Gross written premiums |  | 1,292.5 |  |  | 1,079.1 |  |  | 2,371.6 |
Ceded |  | (124.8 | ) |  | (213.3 | ) |  | (338.1 | )
Net written premiums |  | $ | 1,167.7 |  |  | $ | 865.8 |  |  | $ | 2,033.5 |
Earned premiums: |  |  |  |  |  |
Direct |  | $ | 1,242.5 |  |  | $ | 117.9 |  |  | $ | 1,360.4 |
Assumed |  | 60.7 |  |  | 929.7 |  |  | 990.4 |
Gross earned premiums |  | 1,303.2 |  |  | 1,047.6 |  |  | 2,350.8 |
Ceded |  | (122.1 | ) |  | (199.7 | ) |  | (321.8 | )
Net earned premiums |  | $ | 1,181.1 |  |  | $ | 847.9 |  |  | $ | 2,029.0 |
Losses and LAE: |  |  |  |  |  |
Direct |  | $ | 677.1 |  |  | $ | 59.4 |  |  | $ | 736.5 |
Assumed |  | 45.1 |  |  | 684.4 |  |  | 729.5 |
Gross losses and LAE |  | 722.2 |  |  | 743.8 |  |  | 1,466.0 |
Ceded |  | (36.6 | ) |  | (212.8 | ) |  | (249.4 | )
Net losses and LAE |  | $ | 685.6 |  |  | $ | 531.0 |  |  | $ | 1,216.6 |
Listing of Sirius's top reinsurers | The following table provides a listing of Sirius Group’s top reinsurers based upon recoverable amounts, the percentage of total recoverables and the reinsurer’s A.M. Best Rating.
Top Reinsurers ($ in millions) |  | Balance at December 31, 2012 |  | % of Total |  | A.M. Best Rating(1) |  | % Collateralized
General Reinsurance Corporation |  | $ | 56.2 |  |  | 17 | % |  | A++ |  | — | %
Swiss Re Group |  | 36.4 |  |  | 11 | % |  | A+ |  | 2 | %
Olympus Re (2) |  | 29.6 |  |  | 9 | % |  | NR-5 |  | 100 | %
Lloyds of London (3) |  | 19.4 |  |  | 6 | % |  | A |  | 8 | %
Michigan Catastrophic Claims Association (4) |  | 14.7 |  |  | 4 | % |  | N/A |  | — | %
(1) A.M. Best ratings as detailed above are: “A++” (Superior, which is the highest of 16 financial strength ratings), “A+” (Superior, which is the second highest of 16 financial strength ratings), and “A” (Excellent, which is the third highest of 16 financial strength ratings). (2) Non-U.S. insurance entity. The balance is fully collateralized through funds held, letters of credit or trust agreements. (3) Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates. (4) Michigan Catastrophic Claims Association (”MCCA”) is a non-profit unincorporated association., established by the State of Michigan with the power to issue and collect assessments, to which every insurance company that sells automobile coverage in Michigan is required to be a member. A.M. Best does not rate MCCA. Sirius Group acquired its recoverable from MCCA in the acquisition of Stockbridge Insurance Company. As part of the acquisition, Sirius Group obtained $25.0 of reinsurance protection from the seller (currently rated A+ by A.M. Best) for unfavorable loss reserve development, including uncollectible reinsurance.

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- Definition Tabular disclosure of premiums and losses on a direct assumed and ceded basis. + References No definition available. + Details
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- Definition Tabular disclosure of the top five reinsurers that have assumed business from Sirius based on the amount recoverable from each reinsurer. The disclosure for each reinsurer also includes the amount recoverable as a percentage of Sirius's total reinsurance recoverables, the A.M Best Company, Inc. ("A.M. Best") rating and the percentage of the amount recoverable that is collateralized. + References No definition available. + Details
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