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Exit Activities and Discontinued Operations - Schedule of Retention Benefit Liability Roll Forward (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 18 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2021 | Jun. 30, 2020 | Mar. 31, 2021 | Dec. 31, 2020
Restructuring Reserve [Roll Forward] |  |  |  |  |
Other current liabilities | $ 174 | $ 174 |  |  | $ 133
Retention Benefits | D.E. Karn Generating Complex |  |  |  |  |
Restructuring Reserve [Roll Forward] |  |  |  |  |
Retention benefit liability at beginning of period |  | 11 | $ 4 |  |
Costs incurred and charged to maintenance and other operating expenses |  | 0 | 7 | $ 16 |
Costs deferred as a regulatory asset | 2 | 4 | 0 |  |
Costs incurred and capitalized |  | 0 | 1 |  |
Retention benefit liability at the end of the period | 15 | 15 | 12 |  |
Other current liabilities | $ 5 | $ 5 | $ 5 |  |

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