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Derivatives and Fair Value of Financial Instruments - Fair Value of Investments and Long-Term Debt (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Schedule of amortized cost and estimated fair values of investments and long term debt |  |
Short-term investments, trading debt securities | $ 1,336 | $ 1,576

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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