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Plant, Property, and Equipment (Public Utilities Property Plant and Equipment Schedule of Composite Depreciation Rate Table) (Details) (Consumers Energy Company [Member]) | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Electric Utility Property [Member] |  |  |
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service | 3.20% | 3.00% | 3.00%
Gas Utility Property [Member] |  |  |
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service | 2.90% | 2.90% | 2.90%
Other property [Member] |  |  |
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service | 7.20% | 7.40% | 7.40%

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- Definition Composite depreciation rate for public utility plants in service. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration