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Investments in Unconsolidated Affiliates (Investments in Symetra Table Rollforward) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 10 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Mar. 31, 2015 | Jun. 30, 2016 | Jun. 30, 2015 | Nov. 05, 2015 | Dec. 31, 2015
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Equity in earnings | $ 0.0 | $ 6.8 |  | $ 0.0 | $ 14.1 |  |
Income Tax Expense (Benefit) | $ (6.0) | (2.2) |  | $ (15.7) | 2.4 |  |
Symetra | Common Stock |  |  |  |  |  |  |
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Carrying value at the beginning of the period |  | 447.3 | $ 411.4 |  | 411.4 | $ 411.4 | $ 411.4
Equity in earnings |  | 6.1 |  |  | 13.3 |  |
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio |  | (66.4) |  |  | (35.5) |  |
Dividends received |  | (2.2) | (2.2) |  | (4.4) | $ (4.4) |
Carrying value of a distribution |  | 12.4 |  |  | 12.4 |  |
Carrying value at the end of the period |  | 397.2 | $ 447.3 |  | $ 397.2 |  |
White Mountains | Common Stock |  |  |  |  |  |  |
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio |  | 2.0 |  |  |  |  |
equity in earnings of unconsolidated affiliates | Symetra | Common Stock |  |  |  |  |  |  |
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Income Tax Expense (Benefit) |  | 0.4 |  |  |  |  | 0.8
Net unrealized gains (losses) of unconsolidated affiliates | White Mountains | Common Stock |  |  |  |  |  |  |
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Income Tax Expense (Benefit) |  | 0.0 |  |  |  |  |
Amortization of common share basis difference | Symetra | Common Stock |  |  |  |  |  |  |
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Equity in earnings |  | 0.7 |  |  |  |  | 1.4
impairment of net unrealized gains (losses) | Net unrealized gains (losses) of unconsolidated affiliates | Symetra | Common Stock |  |  |  |  |  |  |
Changes in carrying value of investment in Symetra |  |  |  |  |  |  |
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio |  | $ 2.8 |  |  |  |  | $ 5.7

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