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Investment Securities (Net Realized Investment Gain (losses) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investment securities |  |  |  |
Net realized investment gains (losses), pre-tax |  | $ 96.6 | $ (23.9) | $ 35.3
Net realized investment gains (losses), foreign, pre-tax |  | 0.0 | 11.0 | (11.2)
Net realized investment gains (losses), pre-tax, total |  | 96.6 | (12.9) | 24.1
Income tax expense attributable to net realized investment gains (losses) |  | (10.6) | 9.1 | 8.9
Income tax expense attributable to net realized investment gains (losses), foreign |  | 0.0 | 0.0 | 0.0
Income tax expense attributable to net realized investment gains, total |  | (10.6) | 9.1 | 8.9
Net realized investment gains (losses), after-tax |  | 86.0 | (14.8) | 26.4
Net realized investment gains (losses), foreign, after-tax |  | 0.0 | 11.0 | (11.2)
Net realized investment gains (losses), total, after-tax |  | 86.0 | (3.8) | 15.2
Realized gains |  | 104.0 | 49.4 | 61.5
Realized losses |  | 7.4 | 62.3 | 37.4
Fixed maturity investments |  |  |  |
Investment securities |  |  |  |
Net realized investment gains (losses), pre-tax |  | 4.9 | (29.8) | (1.6)
Net realized investment gains (losses), foreign, pre-tax |  | 0.0 | 18.2 | 4.1
Net realized investment gains (losses), pre-tax, total |  | 4.9 | (11.6) | 2.5
Short-term investments |  |  |  |
Investment securities |  |  |  |
Net realized investment gains (losses), pre-tax |  | 0.2 | (0.8) | (0.3)
Net realized investment gains (losses), foreign, pre-tax |  | 0.0 | 0.0 | 0.0
Net realized investment gains (losses), pre-tax, total |  | 0.2 | (0.8) | (0.3)
Common equity securities |  |  |  |
Investment securities |  |  |  |
Net realized investment gains (losses), pre-tax |  | 85.9 | 6.6 | 18.1
Net realized investment gains (losses), foreign, pre-tax |  | 0.0 | 0.0 | 6.0
Net realized investment gains (losses), pre-tax, total |  | 85.9 | 6.6 | 24.1
Other long-term investments |  |  |  |
Investment securities |  |  |  |
Net realized investment gains (losses), pre-tax |  | 5.6 | 0.1 | 19.1
Net realized investment gains (losses), foreign, pre-tax |  | 0.0 | (7.2) | (21.3)
Net realized investment gains (losses), pre-tax, total |  | 5.6 | $ (7.1) | $ (2.2)
MediaAlpha |  |  |  |
Investment securities |  |  |  |
Realized gain from transaction | $ 67.5 | $ 67.5 |  |

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