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Investment Securities - Insurance-Linked Securities Funds (Details) $ in Millions | 9 Months Ended |  |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 USD ($) fund | Dec. 31, 2019 USD ($) | Sep. 30, 2019 USD ($) | Dec. 31, 2018 USD ($)
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 2,533.4 | $ 2,746.0 | $ 2,569.4 | $ 2,328.7
Minimum |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Redemptions and advanced redemption notice period | 30 days |  |  |
Maximum |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Redemptions and advanced redemption notice period | 90 days |  |  |
Insurance-Linked Securities Funds |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Number of investments | fund | 4 |  |  |
Fair value investments | $ 52.7 |  |  |

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