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Fair Value Measurements and Financial Instruments - Schedule of assets and liabilities that are measured at fair value on a recurring basis (Details) - Recurring - USD ($) $ in Millions | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Money market funds and highly liquid debt securities |  |
Assets: |  |
Money market funds and highly liquid debt securities | $ 1,709 | $ 1,847
Government bonds |  |
Assets: |  |
Other investments: | 1 | 1
Equity investments |  |
Assets: |  |
Other investments: | 3 | 4
Gross foreign exchange contracts |  |
Assets: |  |
Derivatives | 25 | 33
Liabilities: |  |
Derivatives | 10 | 6
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds and highly liquid debt securities |  |
Assets: |  |
Money market funds and highly liquid debt securities | 1,709 | 1,847
Quoted Prices in Active Markets for Identical Assets (Level 1) | Government bonds |  |
Assets: |  |
Other investments: | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity investments |  |
Assets: |  |
Other investments: | 0 | 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Gross foreign exchange contracts |  |
Assets: |  |
Derivatives | 0 | 0
Liabilities: |  |
Derivatives | 0 | 0
Significant Other Observable Inputs (Level 2) | Money market funds and highly liquid debt securities |  |
Assets: |  |
Money market funds and highly liquid debt securities | 0 | 0
Significant Other Observable Inputs (Level 2) | Government bonds |  |
Assets: |  |
Other investments: | 1 | 1
Significant Other Observable Inputs (Level 2) | Equity investments |  |
Assets: |  |
Other investments: | 3 | 4
Significant Other Observable Inputs (Level 2) | Gross foreign exchange contracts |  |
Assets: |  |
Derivatives | 25 | 33
Liabilities: |  |
Derivatives | 10 | 6
Significant Unobservable Inputs (Level 3) | Money market funds and highly liquid debt securities |  |
Assets: |  |
Money market funds and highly liquid debt securities | 0 | 0
Significant Unobservable Inputs (Level 3) | Government bonds |  |
Assets: |  |
Other investments: | 0 | 0
Significant Unobservable Inputs (Level 3) | Equity investments |  |
Assets: |  |
Other investments: | 0 | 0
Significant Unobservable Inputs (Level 3) | Gross foreign exchange contracts |  |
Assets: |  |
Derivatives | 0 | 0
Liabilities: |  |
Derivatives | $ 0 | $ 0

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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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