XML 76 R100.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Pension Plan [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | $ 1,979 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | $ 1,964 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 629 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 558 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 1,350 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 1,406 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Pension Plan [Member] | Cash and Short-Term Investments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 31 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 109 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Cash and Short-Term Investments [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 31 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 109 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Pension Plan [Member] | U.S. Government and Agencies Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 30 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 25 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | U.S. Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 30 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 25 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Pension Plan [Member] | Corporate Debt [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 222 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 188 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 222 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 188 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Pension Plan [Member] | State and Municipal Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 8 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_StateAndMunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 5 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_StateAndMunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 8 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_StateAndMunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 5 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_StateAndMunicipalBondsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Pension Plan [Member] | Foreign Corporate Debt [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 21 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_ForeignCorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 20 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_ForeignCorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Foreign Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 21 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_ForeignCorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 20 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_ForeignCorporateDebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Pension Plan [Member] | Mutual Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 598 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_MutualFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 449 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_MutualFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 598 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_MutualFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 449 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_MutualFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Pension Plan [Member] | Pooled Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 1,069 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_PooledFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 1,168 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_PooledFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 1,069 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_PooledFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 1,168 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_PooledFundsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
OPEB [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 1,265 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 1,218 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
OPEB [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 1,186 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1,141 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 526 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 458 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
OPEB [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 494 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 428 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 739 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 760 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
OPEB [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 692 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 713 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] | Cash and Short-Term Investments [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 19 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 44 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
OPEB [Member] | Cash and Short-Term Investments [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 18 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 41 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] | Cash and Short-Term Investments [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 19 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 44 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
OPEB [Member] | Cash and Short-Term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 18 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 41 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = cms_CashAndShortTermInvestmentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] | U.S. Government and Agencies Securities [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 5 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 3 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
OPEB [Member] | U.S. Government and Agencies Securities [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 4 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 3 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] | U.S. Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined Benefit Plan, Assets for Plan Benefits | 5 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 3 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_USTreasuryAndGovernmentMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
OPEB [Member] | U.S. Government and Agencies Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Corporate Debt [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Corporate Debt [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | State and Municipal Bonds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | State and Municipal Bonds [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | State and Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Foreign Corporate Debt [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Foreign Corporate Debt [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Foreign Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Foreign Corporate Debt [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Common Stocks [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Common Stocks [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Common Stocks [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Mutual Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Mutual Funds [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Pooled Funds [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Pooled Funds [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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OPEB [Member] | Pooled Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
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