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Exit Activities and Discontinued Operations - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 18 Months Ended
--- | --- | --- | ---
Dec. 31, 2021 | Jun. 30, 2021 | Jun. 30, 2020 | Mar. 31, 2021
Discontinued Operations, Held-for-sale | EnerBank | Forecast |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Proceeds from divestiture of businesses | $ 960 |  |  |
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 |  |
Retention and severance costs |  | 0 | $ 7 | $ 16
Costs incurred and capitalized |  | 0 | $ 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 |  | $ 4 |  |
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 |  |  |  | $ 3

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