Retirement Benefits (Schedule Of Pooled Funds Components) (Details)	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
U.S. equity securities	64.00%	61.00%
Foreign equity securities	16.00%	28.00%
U.S. fixed-income securities	9.00%	4.00%
Foreign fixed-income securities	6.00%	3.00%
Alternative investments	5.00%	4.00%
OPEB [Member] \| Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
U.S. equity securities	62.00%	60.00%
Foreign equity securities	12.00%	20.00%
U.S. fixed-income securities	18.00%	14.00%
Foreign fixed-income securities	5.00%	4.00%
Alternative investments	3.00%	2.00%

Alternative investments included in the Pooled funds category of the Plan trust assets.

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Foreign equity securities included in the Pooled funds category of the Plan trust assets.

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Foreign fixed-income securities included in the Pooled funds category of the Plan trust assets.

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U.S. equity securities included in the Pooled funds category of the Plan trust assets.

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U.S. fixed-income securities included in the Pooled funds category of the Plan trust assets.

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