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Plant, Property, and Equipment (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2015 USD ($) MW | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($)
Property, Plant and Equipment [Line Items] |  |  |
Payments to acquire plant | $ 1,564 | $ 1,577 | $ 1,325
Consumers Energy Company [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Payments to acquire plant | $ 1,537 | $ 1,573 | $ 1,320
Gas Fueled Electric Generating Units [Member] | Consumers Energy Company [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Plant capacity | MW | 540 |  |
Payments to acquire plant | $ 155 |  |
Goodwill | 0 |  |
Minimum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Expected future amortization expense of intangible assets, per year | 84 |  |
Minimum [Member] | Consumers Energy Company [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Expected future amortization expense of intangible assets, per year | 84 |  |
Maximum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Expected future amortization expense of intangible assets, per year | 110 |  |
Maximum [Member] | Consumers Energy Company [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Expected future amortization expense of intangible assets, per year | $ 110 |  |

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