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Asset Retirement Obligations (Tables) | 9 Months Ended
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Sep. 30, 2021
Asset Retirement Obligation Disclosure [Abstract] |
Asset retirement obligations |
| Asset Retirement Obligations
(Dollars in millions) |
Balance at December 31, 2020 | $ | 249 |
Additional liabilities accrued | 8 |
Revisions in estimated cash outflows | 43 |
Disposition of assets | (1) |
Accretion expense | 11 |
Balance at September 30, 2021 | $ | 310 |

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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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