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Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Unrealized gains (losses) on investments | $ (10.6) | $ 9.9 | $ 209.6 | $ (28.0)
Net Foreign Exchange Gains, pre-tax | 0.3 | (0.8) | 0.0 | (11.5)
Net unrealized investment gains (losses), pre-tax | (10.3) | 9.1 | 209.6 | (39.5)
Net Unrealized Gains (Losses), tax | (3.0) | 11.4 | (47.5) | 5.1
Net Foreign Exchange Gains, tax | 0.0 | (0.1) | 0.0 | 0.0
Total Net Unrealized Gains (Losses) Reflected in Earnings, tax | (3.0) | 11.3 | (47.5) | 5.1
Net Unrealized Gains (Losses), after-tax | (7.6) | (1.5) | 162.1 | (33.1)
Net Foreign Exchange Gains, after-tax | 0.3 | (0.7) | 0.0 | (11.5)
Total Net Unrealized Gains (Losses) Reflected in Earnings, after-tax | (7.3) | (2.2) | 162.1 | (44.6)
Fixed maturity investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 13.9 | 1.4 | 35.9 | (17.2)
Net Foreign Exchange Gains, pre-tax | 0.0 | 0.0 | 0.0 | (14.8)
Net unrealized investment gains (losses), pre-tax | 13.9 | 1.4 | 35.9 | (32.0)
Short-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 0.2 | 0.7 | 0.2 | 0.0
Net Foreign Exchange Gains, pre-tax | 0.0 | 0.0 | 0.0 | 0.0
Net unrealized investment gains (losses), pre-tax | 0.2 | 0.7 | 0.2 | 0.0
Common equity securities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Unrealized gains (losses) on investments | (13.8) | 5.5 | 71.7 | (11.2)
Net Foreign Exchange Gains, pre-tax | 0.0 | 0.0 | 0.0 | 0.0
Net unrealized investment gains (losses), pre-tax | (13.8) | 5.5 | 71.7 | (11.2)
Other long-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Unrealized gains (losses) on investments | (10.9) | 2.3 | 101.8 | 0.4
Net Foreign Exchange Gains, pre-tax | 0.3 | (0.8) | 0.0 | 3.3
Net unrealized investment gains (losses), pre-tax | $ (10.6) | $ 1.5 | 101.8 | $ 3.7
MediaAlpha |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Unrealized investment gain |  |  | $ 114.7 |

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