| **Goodwill Impairment - Narrative (Details) - USD ($) $ in Millions** | Dec. 31, 2018 | Sep. 30, 2018 | Dec. 31, 2017 |
|-----------------------------------------------------------------------|---------------|---------------|---------------|
| **Goodwill [Line Items]**                                             |          |          |          |
| Goodwill                                                              | $ 110         | $ 1,400       | $ 1,310       |
| Texas                                                                 |          |          |          |
| **Goodwill [Line Items]**                                             |          |          |          |
| Goodwill                                                              |          | $ 1,300       |          |
| Midstream                                                             |          |          |          |
| **Goodwill [Line Items]**                                             |          |          |          |
| Goodwill                                                              | $ 110         |          |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| - Definition
Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266
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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.
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| X                                                                                                                                     |
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