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Summary of Significant Accounting Policies Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2019
Environmental Exit Cost [Line Items] |
Schedule of Asset Retirement Obligations [Table Text Block] | The activity in our asset retirement obligation liability for 2019 and 2018 is summarized in the following table.
Dollar amounts in millions | Year ended December 31,
2019 |  | 2018
Beginning balance | $ | 12 |  |  | $ | 11 |
Accretion expense | 1 |  |  | 1 |
Adjusted to expense during the year | (2 | ) |  | 2 |
Adjusted to other operating credits and charges, net | — |  |  | (1 | )
Ending balance | $ | 11 |  |  | $ | 12 |

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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. + Details
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- Definition Tabular disclosure of the carrying amount of a liability for asset retirement obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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