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Asset Sales and Exit Activities - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended | 15 Months Ended
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |
Regulatory liabilities | $ 151 | $ 87 | $ 151
Electric Utility | Gain shared with customers | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |
Gain on disposition of assets | 14 |  |
Consumers Energy Company |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |
Regulatory liabilities | 151 | 87 | 151
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
Retention and severance costs | 13 | 3 | 16
Costs incurred and capitalized | 2 | 1 |
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
Gain shared with customers | Consumers Energy Company |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |
Regulatory liabilities | $ 14 | $ 17 | $ 14

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