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Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Jun. 30, 2020
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Regulatory assets, noncurrent | $ 2,745 |  | $ 2,745 |  | $ 2,489 |
Regulatory liabilities | 69 |  | 69 |  | 87 |
Revenue | 1,575 | $ 1,546 | 4,882 | $ 5,050 |  |
Consumers Energy Company |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Regulatory assets, noncurrent | 2,745 |  | 2,745 |  | 2,489 |
Regulatory liabilities | 69 |  | 69 |  | 87 |
Revenue | 1,450 | $ 1,429 | 4,524 | $ 4,706 |  |
Gain Shared with Customers for Substation Transmission Assets to METC | Consumers Energy Company |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Regulatory liabilities |  |  |  |  | 17 |
Energy Waste Reduction Plan Incentive | Consumers Energy Company |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Requested recovery collection |  |  |  |  |  | $ 34
Revenue |  |  |  |  | $ 34 |
COVID-19 Costs Accounting Deferral | Consumers Energy Company |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Regulatory assets, noncurrent | $ 5 |  | $ 5 |  |  |

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