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Commitments and Contingencies - Schedule of Company's Restricted Assets (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Sep. 19, 2018 | May 01, 2018 | Dec. 31, 2017
Fair Value, Separate Account Investment [Line Items] |  |  |  |  |
Total restricted assets | $ 4,268.3 | $ 4,419.2 |  |  |
Other investments | $ 111.4 | $ 102.5 |  |  |
Total as percent of investable assets | 54.40% | 56.40% |  |  |
Securities and cash as collateral secured letters of credit | $ 635.4 | $ 771.1 |  |  |
Affiliated transactions |  |  |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |  |  |
Total restricted assets | 754.9 | 1,033.9 |  |  |
Third party |  |  |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |  |  |
Total restricted assets | 2,766.6 | 2,511.7 |  |  |
Letters of credit / guarantees |  |  |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |  |  |
Total restricted assets | 635.4 | 771.1 |  |  |
Limited Partner | Real estate fund |  |  |  |  |
Fair Value, Separate Account Investment [Line Items] |  |  |  |  |
Total restricted assets |  |  |  |  | $ 100.0
Other investments | $ 111.4 | $ 102.5 | $ 13.8 | $ 86.2 |

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