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Investments in Unconsolidated Affiliates (Financial Information) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended |  | 1 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2013 Symetra | Dec. 31, 2012 Symetra | Dec. 31, 2011 Symetra | Dec. 31, 2010 Symetra | Apr. 30, 2007 Pentelia Capital Management | Dec. 31, 2013 Pentelia Capital Management | Dec. 31, 2012 Pentelia Capital Management | Dec. 31, 2011 Pentelia Capital Management | Dec. 31, 2013 Hamer, LLC | Dec. 31, 2012 Hamer, LLC | Sep. 30, 2013 Bri-Mar Manufacturing, LLC | Dec. 31, 2013 Bri-Mar Manufacturing, LLC | Dec. 31, 2012 Bri-Mar Manufacturing, LLC
Symetra balance sheet data; [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total investments |  |  |  |  |  |  |  |  |  |  |  | $ 27,901.1 |  | $ 27,556.4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Separate account assets |  |  |  |  |  |  |  |  |  |  |  | 978.4 |  | 807.7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total assets |  |  |  |  |  |  |  |  |  |  |  | 30,129.5 |  | 29,460.9 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Policyholder liabilities |  |  |  |  |  |  |  |  |  |  |  | 25,328.8 |  | 23,735.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  | 449.5 |  | 449.4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Separate account liabilities |  |  |  |  |  |  |  |  |  |  |  | 978.4 |  | 807.7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total liabilities |  |  |  |  |  |  |  |  |  |  |  | 27,187.6 |  | 25,830.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common shareholders’ equity |  |  |  |  |  |  |  |  |  |  |  | 2,941.9 |  | 3,630.1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Symetra income statement data: [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  |  |  |  | 627.2 |  | 605.0 |  | 540.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net investment income |  |  |  |  |  |  |  |  |  |  |  | 1,285.0 |  | 1,275.2 |  | 1,270.9 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenues |  |  |  |  |  |  |  |  |  |  |  | 2,103.9 | [1] | 2,101.2 | [1] | 1,999.3 | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Policy benefits |  |  |  |  |  |  |  |  |  |  |  | 1,394.9 |  | 1,371.8 |  | 1,307.3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total expenses |  |  |  |  |  |  |  |  |  |  |  | 1,865.3 | [1] | 1,831.1 | [1] | 1,726.1 | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income |  |  |  |  |  |  |  |  |  |  |  | 220.7 | [1] | 205.4 | [1] | 195.8 | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Comprehensive net income |  |  |  |  |  |  |  |  |  |  |  | (777.6) |  | 549.3 |  | 785.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 17.03% |  | 14.60% |  |  |  |  | 33.00% |  |  |  |  |  |  |  |  |  |  |  |
Payments to acquire investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.6 |  |  |  |  |  |  |  |  |  |  |  |
Equity in earnings (losses) of unconsolidated affiliates, net of tax | 11.7 | 8.6 | 7.1 | 9.2 | 5.5 | 7.7 | 6.5 | 10.2 | 36.6 | 29.9 | (20.2) | 37.8 |  | 32.3 | [2],[3],[4] | 28.2 | [2],[3] |  |  | 0.1 | (1.3) | (0.2) | 0.9 |  | 0.4 |  | 0.9 |  |  |  |
Dividends received |  |  |  |  |  |  |  |  |  |  |  | (6.4) |  | (4.9) |  | (4.0) |  |  |  | (0.4) |  |  | (0.8) |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates | 321.4 |  |  |  | 387.9 |  |  |  | 321.4 | 387.9 |  | 317.3 | [2],[5] | 381.5 | [6] | 273.6 | [6] | 387.5 |  | 0 | 0.5 |  | 4.1 | [7] | 4.0 | [7] |  | 0 | [7] | 1.9 | [7]
Proceeds from Sale of Equity Method Investments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.1 |  |  |
Equity Method Investment, Realized Gain (Loss) on Disposal |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.7 |  |  |
[1] | Amounts for the years ended December 31, 2011 have been restated for the effect of Symetra’s adoption of ASU 2010-26.
[2] | Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3
[3] | Equity in earnings for the years end December 31, 2013, 2012 and 2011 includes $.2, $1.3, and $1.0 loss from the dilutive effect of Symetra’s yearly dividend and the issuance of restricted shares by Symetra
[4] | Equity in earnings for the years ended December 31, 2013 and 2012 includes $3.0 and $3.5 increases relating to the pre-tax amortization of the Symetra common share basis difference.
[5] | The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.
[6] | Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0
[7] | As of October 1, 2012, Hamer and Bri-Mar are no longer consolidated and are accounted for as investments in unconsolidated affiliates.

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