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Investments in Marketable Securities (Tables) | 12 Months Ended
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Dec. 31, 2023
Marketable Securities [Abstract] |
Schedule of Investments in Marketable Securities | The following table summarizes the cost, gross unrealized gains, gross unrealized losses, and fair value of investments in equity securities:
|  | December 31,
|  | 2022 |  | 2023
Cost |  | $ | 394.4 |  |  | $ | 35.3 |
Unrealized gains |  | 59.9 |  |  | 2.6 |
Unrealized losses |  | (6.4) |  |  | (0.0 | )
Fair value |  | $ | 447.9 |  |  | $ | 37.9 |
The following table summarizes the cost, unrealized gains, unrealized losses, and fair value of investments in U.S. Treasury securities classified as available-for-sale, all of which mature in 2024, and consolidated Affiliate sponsored investment products classified as trading:
|  | Available-for-Sale |  | Trading
|  | December 31, 2022 |  | December 31, 2023 |  | December 31, 2022 |  | December 31, 2023
Cost |  | $ | 252.3 |  |  | $ | 405.4 |  |  | $ | 19.7 |  |  | $ | 17.9 |
Unrealized gains |  | — |  |  | 0.0 |  |  | — |  |  | — |
Unrealized losses |  | (1.3) |  |  | (0.1) |  |  | (1.7) |  |  | (0.1) |
Fair value |  | $ | 251.0 |  |  | $ | 405.3 |  |  | $ | 18.0 |  |  | $ | 17.8 |

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- Definition Tabular disclosure of marketable securities. This may consist of investments in certain debt and equity securities, short-term investments and other assets. + References No definition available. + Details
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