| **Fair Value Measurements and Disclosures - Fair Value of Equity Method Investments (Details) - USD ($) $ in Millions** | Mar. 31, 2018 | Dec. 31, 2017 |
|-------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                        |          |          |
| Equity owned (units)                                                                                                    | 21,692,198    | 21,692,198    |
| Carrying Amount                                                                                                         |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                        |          |          |
| Investment in CNX Midstream Partners (21,692,198 Units)                                                                 | $ 72          | $ 70          |
| Fair Value                                                                                                              |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                        |          |          |
| Investment in CNX Midstream Partners (21,692,198 Units)                                                                 | $ 399         | $ 364         |

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| - Definition
Fair value portion of investments accounted under the equity method.
+ References
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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.
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| - Definition
Balance held at close of period in number of shares.
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