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Financial Instruments and Risk Management (Tables) | 12 Months Ended
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Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract] |
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments | :
| December 31, 2017 |  | December 31, 2016
Millions of dollars | Level 1 | Level 2 | Total fair value | Carrying value |  | Level 1 | Level 2 | Total fair value | Carrying value
Total debt | $ | 3,285 |  | $ | 9,172 |  | $ | 12,457 |  | $ | 10,942 |  |  | $ | 753 |  | $ | 12,812 |  | $ | 13,565 |  | $ | 12,384 |

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- Definition Tabular disclosure of information pertaining to carrying amount and estimated fair value of short-term and long-term debt instruments or arrangements, including but not limited to, identification of terms, features, and collateral requirements. + References No definition available. + Details
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