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Revenue (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |  |  |  |
Uncollectable expense | $ 5 | $ 9 | $ 18 | $ 21 |
Regulatory assets | 2,745 |  | 2,745 |  | $ 2,489
Consumers Energy Company |  |  |  |  |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |  |  |  |
Regulatory assets | 2,745 |  | 2,745 |  | 2,489
Unbilled receivables | 267 |  | 267 |  | $ 426
COVID-19 Costs Accounting Deferral | Consumers Energy Company |  |  |  |  |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |  |  |  |
Regulatory assets | $ 5 |  | $ 5 |  |

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