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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract] |
Reconciliation of Changes in Asset Retirement Obligations [Table Text Block] | The following is a reconciliation of the changes in the ARO from January 1, 2017 to December 31, 2018:
(In millions) | 2018 |  | 2017
AROs at beginning of period | $ | 28 |  |  | $ | 25 |
Liabilities incurred | 1 |  |  | 2 |
Accretion expense | 1 |  |  | 1 |
AROs at end of period | $ | 30 |  |  | $ | 28 |

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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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