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Investments in Unconsolidated Affiliates (Symetra & Hamer Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2015 | Jun. 30, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Investments in unconsolidated affiliates |  |  |  |  |
Unrealized investment gains |  |  | $ 97.5 | $ (294.7) | $ 235.5
Unrealized investment gains after tax |  |  | 93.5 | (246.4) | 194.2
Equity in earnings of unconsolidated affiliates |  |  | $ 0.0 | $ 0.0 | $ 25.1
Symetra |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |
Unrealized investment gains | $ 258.8 |  |  |  |
Unrealized investment gains after tax | $ 241.1 |  |  |  |
Hamer |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |
Gain on disposal of equity method investment |  | $ 20.0 |  |  |
Equity in earnings of unconsolidated affiliates |  | $ 1.6 |  |  |

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