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v3.19.3.a.u2

Asset Retirement Obligation (Tables) | 12 Months Ended
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Dec. 31, 2019
Asset Retirement Obligation [Abstract] |
Asset retirement obligations | The results of the reviews (identified as Revisions in estimated cash outflows) and other changes in asset retirement obligations during 2019 and 2018, were as follows:
| 2019 |  | 2018
(Dollars in millions) |  |  |
Balance at beginning of year | $ | 307 |  |  | $ | 283 |
Additional liabilities accrued | 13 |  |  | 2 |
Revisions in estimated cash outflows | 2 |  |  | 6 |
Acquisition of assets | 1 |  |  | — |
Disposition of assets | (1 | ) |  | (1 | )
Accretion expense | 20 |  |  | 18 |
Transferred to Liabilities held for sale | — |  |  | (1 | )
Balance at end of year | $ | 342 |  |  | $ | 307 |

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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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