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Debt (Estimated Fair Value of Significant Financial Instruments) (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term debt | $ 638 | $ 262
Long-term debt | 5,512 | 5,225
Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Short-term debt | 637 | 264
Long-term debt | $ 5,477 | $ 5,444

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- Definition Long Term Debt and Capital Lease Obligation, Noncurrent, Fair Value + References No definition available. + Details
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