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Exit Activities and Discontinued Operations - Narrative (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended | 24 Months Ended
--- | --- | --- | --- | ---
Oct. 01, 2021 | Dec. 31, 2021 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021
Discontinued Operations, Held-for-sale | EnerBank |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |
Gain from divestiture of business |  |  | $ (3) | $ 0 | $ (8) | $ 0 |
Discontinued Operations, Held-for-sale | EnerBank | Subsequent Event |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |
Proceeds from divestiture of businesses | $ 1,000 |  |  |  |  |  |
Discontinued Operations, Held-for-sale | EnerBank | Forecast | Subsequent Event |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |
Gain from divestiture of business |  | $ 660 |  |  |  |  |
Retention Benefits | D.E. Karn Generating Complex |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |
Expected cost |  |  | 35 |  | 35 |  | $ 35
Retention and severance costs |  |  |  |  | 0 | 11 | 16
Costs incurred and capitalized |  |  |  |  | 1 | $ 1 |
Retention Benefits | D.E. Karn Generating Complex | Retention Incentive Program |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |
Regulatory asset |  |  | $ 5 |  | $ 5 |  | 5
Retention Benefits | D.E. Karn Generating Complex | Property, Plant and Equipment |  |  |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |
Costs incurred and capitalized |  |  |  |  |  |  | $ 4

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