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Retirement Benefits (Schedule Of SERP Trust Assets, ABO And Contributions) (Details) (DB SERP [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2013 | Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items] |  |
ABO | $ 122 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation | $ 145 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Contributions | 16 cms_ContributionsMadeToPlan |
Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
ABO | 82 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 99 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Contributions | 13 cms_ContributionsMadeToPlan / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |
DB SERP Trust Assets [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Trust assets | 136 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_DbSerpTrustAssetsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 131 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_DbSerpTrustAssetsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
DB SERP Trust Assets [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Trust assets | $ 96 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_DbSerpTrustAssetsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | $ 93 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_DbSerpTrustAssetsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember

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- Definition Contributions made to the plan Trust fund. + References No definition available. + Details
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- Definition For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503844 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930 + Details
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