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Revenue (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Disaggregation of Revenue [Line Items] |  |  |
Bad debt expense | $ 22 | $ 30 | $ 30
Unbilled receivables | 486 | 437 |
Regulatory liabilities | 146 | 151 |
Consumers Energy Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Bad debt expense | 22 | 33 | 29
Unbilled receivables | 486 | 437 |
Regulatory liabilities | 146 | 151 |
Consumers Energy Company | Reserve for customer refunds |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Regulatory liabilities | 2 | 28 |
Accounts Receivable |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Bad debt expense | 22 | 33 | 29
Accounts Receivable | Consumers Energy Company |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Bad debt expense | $ 22 | $ 33 | $ 29

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