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Other Investments - Investments without Readily Determinable Fair Value (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2021 | Dec. 31, 2020
Investments, All Other Investments [Abstract] |  |  |
Cost | $ 8.5 | $ 8.5 | $ 8.5
Cumulative upward adjustments | 25.0 | 25.0 | 5.3
Carrying amount | 33.5 | 33.5 | $ 13.8
Upward adjustments | $ 19.7 | $ 19.7 |

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