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Investment Securities - Lloyd's Trust Deposits, Bank Loan Fund, and Insurance-Linked Securities Funds (Details) - USD ($) $ in Millions | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020 | Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 3,232.6 | $ 2,796.2 | $ 2,541.6 | $ 2,746.0
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 |  |  |
ILS funds |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 53.8 |  |  |
Lloyds Bank |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 99.2 |  |  |
Bank loan fund |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 89.2 |  |  |

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