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Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Available-for-sale debt securities: |  |
Available-for-sale debt securities | $ 6,614.9 | $ 3,689.1
Corporate bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 5,924.8 | 3,090.3
U.S. government and government agency obligations |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 101.7 | 128.9
Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 65.1 | 66.3
Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 272.6 | 276.1
Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 231.7 | 127.5
Asset-backed securities |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 19.0 |
Measured on a recurring basis |  |
Available-for-sale debt securities: |  |
Total marketable securities | 7,986.5 | 4,528.9
Measured on a recurring basis | Unrestricted |  |
Available-for-sale debt securities: |  |
Equity securities | 35.7 | 48.3
Measured on a recurring basis | Restricted |  |
Available-for-sale debt securities: |  |
Equity securities | 1,335.9 | 791.5
Measured on a recurring basis | Corporate bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 5,924.8 | 3,090.3
Measured on a recurring basis | U.S. government and government agency obligations |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 101.7 | 128.9
Measured on a recurring basis | Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 65.1 | 66.3
Measured on a recurring basis | Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 272.6 | 276.1
Measured on a recurring basis | Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 231.7 | 127.5
Measured on a recurring basis | Asset-backed securities |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 19.0 |
Measured on a recurring basis | Level 1 |  |
Available-for-sale debt securities: |  |
Total marketable securities | 1,371.6 | 839.8
Measured on a recurring basis | Level 1 | Unrestricted |  |
Available-for-sale debt securities: |  |
Equity securities | 35.7 | 48.3
Measured on a recurring basis | Level 1 | Restricted |  |
Available-for-sale debt securities: |  |
Equity securities | 1,335.9 | 791.5
Measured on a recurring basis | Level 1 | Corporate bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 0.0 | 0.0
Measured on a recurring basis | Level 1 | U.S. government and government agency obligations |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 0.0 | 0.0
Measured on a recurring basis | Level 1 | Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 0.0 | 0.0
Measured on a recurring basis | Level 1 | Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 0.0 | 0.0
Measured on a recurring basis | Level 1 | Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 0.0 | 0.0
Measured on a recurring basis | Level 1 | Asset-backed securities |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 0.0 |
Measured on a recurring basis | Level 2 |  |
Available-for-sale debt securities: |  |
Total marketable securities | 6,614.9 | 3,689.1
Measured on a recurring basis | Level 2 | Unrestricted |  |
Available-for-sale debt securities: |  |
Equity securities | 0.0 | 0.0
Measured on a recurring basis | Level 2 | Restricted |  |
Available-for-sale debt securities: |  |
Equity securities | 0.0 | 0.0
Measured on a recurring basis | Level 2 | Corporate bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 5,924.8 | 3,090.3
Measured on a recurring basis | Level 2 | U.S. government and government agency obligations |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 101.7 | 128.9
Measured on a recurring basis | Level 2 | Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 65.1 | 66.3
Measured on a recurring basis | Level 2 | Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 272.6 | 276.1
Measured on a recurring basis | Level 2 | Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 231.7 | $ 127.5
Measured on a recurring basis | Level 2 | Asset-backed securities |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | $ 19.0 |

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