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Income Taxes (Narrative) (Details) - Consumers Energy Company [Member] - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2015 | Jun. 30, 2014
Income Tax Benefits [Line Items] |  |
Reduction of income tax expense | $ 20 | $ 23
Electric Utility [Member] |  |
Income Tax Benefits [Line Items] |  |
Income tax benefits, to be returned to customers | $ 209 |
Tax benefit, distribution to customers, term | 5 years |
Gas Utility [Member] |  |
Income Tax Benefits [Line Items] |  |
Income tax benefits, to be returned to customers | $ 260 |
Tax benefit, distribution to customers, term | 12 years |

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- Details
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