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Regulatory Matters (Schedule of GCR Reconciliation Filing Pending with the MPSC) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2012 Consumers Energy Company [Member] | Dec. 31, 2011 Consumers Energy Company [Member] | Dec. 31, 2010 Consumers Energy Company [Member] | Mar. 31, 2012 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member] | Mar. 31, 2011 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member] | Mar. 31, 2010 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member]
Date Of Filing |  |  |  |  |  |  | June 2012 |  |
Net Over/(Under) Recovery, Including Interest, Requested by Consumers |  |  |  |  |  |  | $ 2 |  |
Cost of gas sold | $ 1,150 | $ 1,512 | $ 1,590 | $ 1,110 | $ 1,438 | $ 1,516 | $ 900 | $ 1,200 | $ 1,300

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- Definition Date of Filing + References No definition available. + Details
Name: | cms_DateOfFiling
Namespace Prefix: | cms_
Data Type: | invest:dateStringItemType
Balance Type: | na
Period Type: | duration

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- Definition Net over-/(under-) recovery of expense, including interest, requested by Consumers. + References No definition available. + Details
Name: | cms_NetOverUnderRecoveryOfExpenseIncludingInterestRequestedByConsumers
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Cost of natural gas purchased and associated transportation and storage costs during the period. + References No definition available. + Details
Name: | us-gaap_CostOfNaturalGasPurchases
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration