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Revenue (Narrative) (Details) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |
Uncollectable expense | $ 14 |
Unbilled receivables | 280 | $ 481
Consumers Energy Company |  |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |  |
Uncollectable expense | 14 |
Unbilled receivables | $ 280 | $ 481

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