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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract] |
Schedule of Asset Retirement Obligations [Table Text Block] | AROs consist of the following (in millions):
| As of December 31,
| 2020 |  | 2019
Trojan decommissioning activities | $ | 139 |  |  | $ | 137 |
Utility plant | 118 |  |  | 126 |
Non-utility property | 34 |  |  | 16 |
Total asset retirement obligations | 291 |  |  | 279 |
Less: current portion * | 21 |  |  | 16 |
Noncurrent asset retirement obligations | $ | 270 |  |  | $ | 263 |
* Current portion of AROs are classified within Accrued expenses and other current liabilities in the consolidated balance sheets.
Schedule of Change in Asset Retirement Obligation [Table Text Block] | The following is a summary of the changes in the Company’s AROs (in millions):
| Years Ended December 31,
| 2020 |  | 2019 |  | 2018
Balance as of beginning of year | $ | 279 |  |  | $ | 197 |  |  | $ | 167 |
Liabilities incurred | 3 |  |  | — |  |  | — |
Liabilities settled | (18) |  |  | (9) |  |  | (5) |
Accretion expense | 10 |  |  | 9 |  |  | 8 |
Revisions in estimated cash flows | 17 |  |  | 82 |  |  | 27 |
Balance as of end of year | $ | 291 |  |  | $ | 279 |  |  | $ | 197 |

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