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Revenue (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021 | Dec. 31, 2021
Disaggregation of Revenue [Line Items] |  |  |  |  |
Unbilled receivables | $ 387 |  | $ 387 |  | $ 486
Consumers Energy Company |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Unbilled receivables | 387 |  | 387 |  | $ 486
Accounts Receivable |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Bad debt expense | 14 | $ 5 | 18 | $ 11 |
Accounts Receivable | Consumers Energy Company |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |
Bad debt expense | $ 14 | $ 5 | $ 18 | $ 11 |

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