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Fair Value Measurements (Details) - USD ($) $ in Millions | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | --- | --- | --- | --- | ---
Assets: |  |  |  |  |  |
Marketable debt securities | $ 2,538.1 |  | $ 3,689.3 |  |  |
Fair Value, Measurements, Recurring |  |  |  |  |  |
Assets: |  |  |  |  |  |
Cash equivalents | 1,120.4 |  | 705.5 |  |  |
Marketable equity securities | 510.0 |  | 615.4 |  |  |
Derivative contracts | 88.2 |  | 66.9 |  |  |
Plan assets for deferred compensation | 29.5 |  | 25.4 |  |  |
Total | 4,286.2 |  | 5,102.5 |  |  |
Liabilities: |  |  |  |  |  |
Derivative contracts | 17.5 |  | 24.6 |  |  |
Contingent consideration obligations | 401.3 | $ 421.3 | 409.8 | $ 499.9 | $ 498.0 | $ 523.6
Total | 418.8 |  | 434.4 |  |  |
Fair Value, Measurements, Recurring | Corporate debt securities |  |  |  |  |  |
Assets: |  |  |  |  |  |
Marketable debt securities | 1,687.7 |  | 2,459.2 |  |  |
Fair Value, Measurements, Recurring | Government securities |  |  |  |  |  |
Assets: |  |  |  |  |  |
Marketable debt securities | 604.4 |  | 969.6 |  |  |
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities |  |  |  |  |  |
Assets: |  |  |  |  |  |
Marketable debt securities | 246.0 |  | 260.5 |  |  |
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |  |
Assets: |  |  |  |  |  |
Cash equivalents | 0.0 |  | 0.0 |  |  |
Marketable equity securities | 176.6 |  | 51.7 |  |  |
Derivative contracts | 0.0 |  | 0.0 |  |  |
Plan assets for deferred compensation | 0.0 |  | 0.0 |  |  |
Total | 176.6 |  | 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 | 1,120.4 |  | 705.5 |  |  |
Marketable equity securities | 333.4 |  | 563.7 |  |  |
Derivative contracts | 88.2 |  | 66.9 |  |  |
Plan assets for deferred compensation | 29.5 |  | 25.4 |  |  |
Total | 4,109.6 |  | 5,050.8 |  |  |
Liabilities: |  |  |  |  |  |
Derivative contracts | 17.5 |  | 24.6 |  |  |
Contingent consideration obligations | 0.0 |  | 0.0 |  |  |
Total | 17.5 |  | 24.6 |  |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities |  |  |  |  |  |
Assets: |  |  |  |  |  |
Marketable debt securities | 1,687.7 |  | 2,459.2 |  |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities |  |  |  |  |  |
Assets: |  |  |  |  |  |
Marketable debt securities | 604.4 |  | 969.6 |  |  |
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities |  |  |  |  |  |
Assets: |  |  |  |  |  |
Marketable debt securities | 246.0 |  | 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 | 401.3 |  | 409.8 |  |  |
Total | 401.3 |  | 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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