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Regulatory Matters (Schedule of the Components of PSCR and GCR Over/(Under) Recoveries) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Accrued gas revenue | $ 27 us-gaap_DeferredFuelCost |
Accrued rate refunds | 6 cms_AccruedRateRefunds | 12 cms_AccruedRateRefunds
Consumers Energy Company [Member] |  |
Accrued gas revenue | 27 us-gaap_DeferredFuelCost / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |
Accrued rate refunds | $ 6 cms_AccruedRateRefunds / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | $ 12 cms_AccruedRateRefunds / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember

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- Definition Current liabilities that represent obligations to make refunds to customers for fuel costs. + References No definition available. + Details
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Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Carrying amount as of the balance sheet date of capitalized fuel costs of a regulated entity that are expected to be recoverable through rate adjustments within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499739&loc=d3e43603-110378 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |