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Equity-Method Eligible Investments - Carrying Values of Equity Method Eligible Investments Recorded within Other Long-Term Investments (Details) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020 | May 07, 2020 | May 06, 2020
--- | --- | --- | --- | ---
Investments in unconsolidated affiliates |  |  |  |
Other long-term investments | $ 1,081.4 | $ 786.8 |  |
Marketing Technology (MediaAlpha) |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Ownership interest (as a percent) | 28.40% | 35.00% |  |
Other long-term investments | $ 713.2 | $ 802.2 |  |
Kudu Investments |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Other long-term investments | $ 455.5 | $ 400.6 |  |
Kudu Investments | Minimum |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Ownership interest (as a percent) | 3.20% | 3.20% |  |
Kudu Investments | Maximum |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Ownership interest (as a percent) | 32.70% | 35.00% |  |
PassportCard/DavidShield |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Ownership interest (as a percent) | 53.80% | 53.80% | 53.80% | 50.00%
Other long-term investments | $ 95.0 | $ 95.0 |  |
Elementum Holdings L.P. |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Ownership interest (as a percent) | 29.70% | 28.90% |  |
Other long-term investments | $ 56.7 | $ 55.1 |  |
Other |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Other long-term investments | 100.9 | 132.2 |  |
Equity Method Investments |  |  |  |
Investments in unconsolidated affiliates |  |  |  |
Other long-term investments | $ 16.6 | $ 15.2 |  |

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