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Fair Value Measurements (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018 | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | --- | --- | ---
Assets: |  |  |  |
Marketable debt securities | $ 3,038.5 | $ 3,689.3 |  |
Fair Value, Measurements, Recurring |  |  |  |
Assets: |  |  |  |
Cash equivalents | 1,881.9 | 705.5 |  |
Marketable equity securities | 904.0 | 615.4 |  |
Derivative contracts | 104.4 | 66.9 |  |
Plan assets for deferred compensation | 29.4 | 25.4 |  |
Total | 5,958.2 | 5,102.5 |  |
Liabilities: |  |  |  |
Derivative contracts | 24.1 | 24.6 |  |
Contingent consideration obligations | 421.3 | 409.8 | $ 498.0 | $ 523.6
Total | 445.4 | 434.4 |  |
Fair Value, Measurements, Recurring | Corporate debt securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 1,835.7 | 2,459.2 |  |
Fair Value, Measurements, Recurring | Government securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 921.3 | 969.6 |  |
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 281.5 | 260.5 |  |
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |
Assets: |  |  |  |
Cash equivalents | 0.0 | 0.0 |  |
Marketable equity securities | 19.5 | 51.7 |  |
Derivative contracts | 0.0 | 0.0 |  |
Plan assets for deferred compensation | 0.0 | 0.0 |  |
Total | 19.5 | 51.7 |  |
Liabilities: |  |  |  |
Derivative contracts | 0.0 | 0.0 |  |
Contingent consideration obligations | 0.0 | 0.0 |  |
Total | 0.0 | 0.0 |  |
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Corporate debt securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 0.0 | 0.0 |  |
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Government securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 0.0 | 0.0 |  |
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 0.0 | 0.0 |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |
Assets: |  |  |  |
Cash equivalents | 1,881.9 | 705.5 |  |
Marketable equity securities | 884.5 | 563.7 |  |
Derivative contracts | 104.4 | 66.9 |  |
Plan assets for deferred compensation | 29.4 | 25.4 |  |
Total | 5,938.7 | 5,050.8 |  |
Liabilities: |  |  |  |
Derivative contracts | 24.1 | 24.6 |  |
Contingent consideration obligations | 0.0 | 0.0 |  |
Total | 24.1 | 24.6 |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 1,835.7 | 2,459.2 |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 921.3 | 969.6 |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 281.5 | 260.5 |  |
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |
Assets: |  |  |  |
Cash equivalents | 0.0 | 0.0 |  |
Marketable equity securities | 0.0 | 0.0 |  |
Derivative contracts | 0.0 | 0.0 |  |
Plan assets for deferred compensation | 0.0 | 0.0 |  |
Total | 0.0 | 0.0 |  |
Liabilities: |  |  |  |
Derivative contracts | 0.0 | 0.0 |  |
Contingent consideration obligations | 421.3 | 409.8 |  |
Total | 421.3 | 409.8 |  |
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate debt securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 0.0 | 0.0 |  |
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Government securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | 0.0 | 0.0 |  |
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities |  |  |  |
Assets: |  |  |  |
Marketable debt securities | $ 0.0 | $ 0.0 |  |

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