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Financial Instruments - Summary of Marketable Securities (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 2,049.1 | $ 2,965.0
Gross Unrealized Gains | 2.3 | 6.0
Gross Unrealized Losses | (0.4) | (0.7)
Fair Value | 2,051.0 | 2,970.3
Corporate debt securities Current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 897.8 | 1,057.2
Gross Unrealized Gains | 0.4 | 1.0
Gross Unrealized Losses | (0.2) | 0.0
Fair Value | 898.0 | 1,058.2
Corporate debt securities Non-current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 402.5 | 633.9
Gross Unrealized Gains | 1.1 | 3.0
Gross Unrealized Losses | (0.1) | 0.0
Fair Value | 403.5 | 636.9
Government securities Current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 380.6 | 502.9
Gross Unrealized Gains | 0.1 | 0.4
Gross Unrealized Losses | 0.0 | 0.0
Fair Value | 380.7 | 503.3
Government securities Non-current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 245.9 | 510.1
Gross Unrealized Gains | 0.5 | 0.8
Gross Unrealized Losses | 0.0 | (0.3)
Fair Value | 246.4 | 510.6
Mortgage and other asset backed securities Current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 0.2 | 0.7
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | 0.0 | 0.0
Fair Value | 0.2 | 0.7
Mortgage and other asset backed securities Non-current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 122.1 | 260.2
Gross Unrealized Gains | 0.2 | 0.8
Gross Unrealized Losses | (0.1) | (0.4)
Fair Value | 122.2 | 260.6
Marketable equity securities, current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Marketable equity securities, amortized cost | 70.6 |
Marketable equity securities, gross unrealized gains | 15.9 |
Marketable equity securities, gross unrealized losses | 0.0 |
Marketable equity securities, fair value | 86.5 |
Marketable equity securities, non-current |  |
Debt Securities, Available-for-sale [Line Items] |  |
Marketable equity securities, amortized cost | 1,168.9 | 218.4
Marketable equity securities, gross unrealized gains | 733.8 | 132.1
Marketable equity securities, gross unrealized losses | (14.9) | (13.0)
Marketable equity securities, fair value | $ 1,887.8 | $ 337.5

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