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Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Available-for-sale debt securities: |  |
Available-for-sale debt securities | $ 4,607.2 | $ 3,689.1
Corporate bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 3,632.2 | 3,090.3
U.S. government and government agency obligations |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 487.8 | 128.9
Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 65.7 | 66.3
Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 254.3 | 276.1
Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 167.2 | 127.5
Measured on a recurring basis | Level 1 |  |
Available-for-sale debt securities: |  |
Total marketable securities | 1,002.4 | 839.8
Measured on a recurring basis | Level 1 | Unrestricted |  |
Available-for-sale debt securities: |  |
Equity securities | 77.7 | 48.3
Measured on a recurring basis | Level 1 | Restricted |  |
Available-for-sale debt securities: |  |
Equity securities | 924.7 | 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 2 |  |
Available-for-sale debt securities: |  |
Total marketable securities | 4,607.2 | 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 | 3,632.2 | 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 | 487.8 | 128.9
Measured on a recurring basis | Level 2 | Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 65.7 | 66.3
Measured on a recurring basis | Level 2 | Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 254.3 | 276.1
Measured on a recurring basis | Level 2 | Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 167.2 | 127.5
Measured on a recurring basis | Estimate of Fair Value Measurement |  |
Available-for-sale debt securities: |  |
Total marketable securities | 5,609.6 | 4,528.9
Measured on a recurring basis | Estimate of Fair Value Measurement | Unrestricted |  |
Available-for-sale debt securities: |  |
Equity securities | 77.7 | 48.3
Measured on a recurring basis | Estimate of Fair Value Measurement | Restricted |  |
Available-for-sale debt securities: |  |
Equity securities | 924.7 | 791.5
Measured on a recurring basis | Estimate of Fair Value Measurement | Corporate bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 3,632.2 | 3,090.3
Measured on a recurring basis | Estimate of Fair Value Measurement | U.S. government and government agency obligations |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 487.8 | 128.9
Measured on a recurring basis | Estimate of Fair Value Measurement | Sovereign bonds |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 65.7 | 66.3
Measured on a recurring basis | Estimate of Fair Value Measurement | Commercial paper |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | 254.3 | 276.1
Measured on a recurring basis | Estimate of Fair Value Measurement | Certificates of deposit |  |
Available-for-sale debt securities: |  |
Available-for-sale debt securities | $ 167.2 | $ 127.5

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