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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2018
Accounting Policies [Abstract] |
Schedule of Change in Asset Retirement Obligation | The following table presents the change in the liability for asset retirement obligations, of which $107 million, $99 million and $33 million were reflected in “Other long-term liabilities and deferred credits” with the remaining portion reflected in “Other current liabilities” on our Consolidated Balance Sheets as of December 31, 2018, 2017 and 2016, respectively (in millions):
| December 31,
| 2018 |  | 2017 |  | 2016
Beginning balance | $ | 103 |  |  | $ | 44 |  |  | $ | 35 |
Liabilities incurred | 3 |  |  | 33 |  |  | 20 |
Liabilities settled | (3 | ) |  | (4 | ) |  | (3 | )
Accretion expense | 4 |  |  | 3 |  |  | 1 |
Revisions in estimated cash flows | 2 |  |  | 27 |  |  | (9 | )
Ending balance | $ | 109 |  |  | $ | 103 |  |  | $ | 44 |

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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