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

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