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Retirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | $ 32 us-gaap_PensionAndOtherPostretirementBenefitContributions |  | $ 229 us-gaap_PensionAndOtherPostretirementBenefitContributions |  | $ 72 us-gaap_PensionAndOtherPostretirementBenefitContributions
Union employees percentage | 41.00%cms_UnionMembershipByTotalEmployeesPercentage |  |  |  |
Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 29 us-gaap_PensionAndOtherPostretirementBenefitContributions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 222 us-gaap_PensionAndOtherPostretirementBenefitContributions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 68 us-gaap_PensionAndOtherPostretirementBenefitContributions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Union employees percentage | 43.00%cms_UnionMembershipByTotalEmployeesPercentage / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Pension Plan [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Trust assets | 1,979 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 1,964 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | 1,727 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Estimated time of amortization of gains losses | 10 years |  | 10 years |  | 11 years
Postretirement benefits contributions |  |  | 150 us-gaap_PensionAndOtherPostretirementBenefitContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | [1] |
Actuarial loss | 458 us-gaap_DefinedBenefitPlanActuarialGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  | (308)us-gaap_DefinedBenefitPlanActuarialGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |
Pension Plan [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated time of amortization of gains losses | 10 years |  | 10 years |  | 11 years
Postretirement benefits contributions |  |  | 147 us-gaap_PensionAndOtherPostretirementBenefitContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [1] |
OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Trust assets | 1,265 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | 1,218 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | 1,047 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Retirement age requirement | 55 cms_RetirementAgeRequirement / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | 55 cms_RetirementAgeRequirement / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | 55 cms_RetirementAgeRequirement / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Retirement years of service | 10 years |  |  |  |
Retirement years of service with disability | 15 years |  |  |  |
Health care cost trend rate assumed for next fiscal year | 6.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | 6.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |
Ultimate health care cost trend rate | 4.75%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |  |
Year that rate reaches ultimate trend rate | 2024 |  |  |  |
Estimated time of amortization of gains losses | 13 years |  | 13 years |  | 13 years
Estimated time of prior service cost |  |  | 10 years |  |
Postretirement benefits contributions | 25 us-gaap_PensionAndOtherPostretirementBenefitContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [2] | 72 us-gaap_PensionAndOtherPostretirementBenefitContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | [2] |
Estimated future employer contributions | 29 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |  |  |
Actuarial loss | 230 us-gaap_DefinedBenefitPlanActuarialGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  | (440)us-gaap_DefinedBenefitPlanActuarialGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |
OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Trust assets | 1,186 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 1,141 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 978 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Retirement age requirement | 55 cms_RetirementAgeRequirement / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 55 cms_RetirementAgeRequirement / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 55 cms_RetirementAgeRequirement / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Retirement years of service | 10 years |  |  |  |
Retirement years of service with disability | 15 years |  |  |  |
Health care cost trend rate assumed for next fiscal year | 6.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 6.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Ultimate health care cost trend rate | 4.75%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Year that rate reaches ultimate trend rate | 2024 |  |  |  |
Estimated time of amortization of gains losses | 13 years |  | 13 years |  | 13 years
Estimated time of prior service cost |  |  | 10 years |  |
Postretirement benefits contributions | 25 us-gaap_PensionAndOtherPostretirementBenefitContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] | 71 us-gaap_PensionAndOtherPostretirementBenefitContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] |
Estimated future employer contributions | 29 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Actuarial loss | 223 us-gaap_DefinedBenefitPlanActuarialGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | (424)us-gaap_DefinedBenefitPlanActuarialGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Pension And OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Amortized net gains and losses in excess of PBO or MRV | 10.00%cms_AmortizedNetGainsAndLossesInExcessOfPboOrMrv / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndOpebMember |  | 10.00%cms_AmortizedNetGainsAndLossesInExcessOfPboOrMrv / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndOpebMember |  | 10.00%cms_AmortizedNetGainsAndLossesInExcessOfPboOrMrv / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndOpebMember
Pension And OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Amortized net gains and losses in excess of PBO or MRV | 10.00%cms_AmortizedNetGainsAndLossesInExcessOfPboOrMrv / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndOpebMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 10.00%cms_AmortizedNetGainsAndLossesInExcessOfPboOrMrv / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndOpebMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 10.00%cms_AmortizedNetGainsAndLossesInExcessOfPboOrMrv / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndOpebMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Defined Company Contribution Plan [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer contribution, percentage of base pay | 6.00%cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember |  | 6.00%cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember |  | 6.00%cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember
Plan cost, defined contribution plan | 13 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember |  | 10 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember |  | 8 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember
Defined Company Contribution Plan [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer contribution, percentage of base pay | 6.00%cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 6.00%cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 6.00%cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Plan cost, defined contribution plan | 13 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 10 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 8 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_DefinedCompanyContributionPlanMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
DC SERP [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Minimum years of participation before vesting | 5 years |  |  |  |
Trust assets | 2 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember |  | 1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember |  |
DC SERP [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Minimum years of participation before vesting | 5 years |  |  |  |
Trust assets | 2 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 1 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
401 (K) Plan [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer match of eligible contributions | 60.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember |  | 60.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember |  | 60.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember
Employer match of eligible wages | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember |  | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember |  | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember
Savings plan, cost recognized | 18 cms_SavingsPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember |  | 17 cms_SavingsPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember |  | 16 cms_SavingsPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember
401 (K) Plan [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer match of eligible contributions | 60.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 60.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 60.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Employer match of eligible wages | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Savings plan, cost recognized | 18 cms_SavingsPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 17 cms_SavingsPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 16 cms_SavingsPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_Plan401KMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Minimum [Member] | DC SERP [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan contribution percentage | 5.00%cms_PlanContributionPercentage / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |
Minimum [Member] | DC SERP [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan contribution percentage | 5.00%cms_PlanContributionPercentage / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |  |
Maximum [Member] | DC SERP [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan cost, defined contribution plan | 1 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | 1 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | 1 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Plan contribution percentage | 15.00%cms_PlanContributionPercentage / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
Maximum [Member] | DC SERP [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan cost, defined contribution plan | $ 1 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | $ 1 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | $ 1 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Plan contribution percentage | 15.00%cms_PlanContributionPercentage / us-gaap_DefinedContributionPlanNameAxis = cms_SupplementalEmployeeRetirementPlanDefinedContributionMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |
[1] | Neither CMS Energy nor Consumers plans to contribute to the DB Pension Plan in 2015.
[2] | CMS Energy, including Consumers, plans to contribute $29 million to the OPEB Plan in 2015, of which Consumers plans to contribute $29 million.

X
- Definition Amortization of gains and losses in excess of ten percent of the greater of the PBO or the MRV over the average remaining service period. + References No definition available. + Details
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Namespace Prefix: | cms_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of base pay that the employer contributes. + References No definition available. + Details
Name: | cms_DefinedContributionPlanEmployerContirbutionsPercentageOfBasePay
Namespace Prefix: | cms_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated time of amortization of gains and losses in excess of ten percent of the greater of the PBO or the MRV over the average remaining service period. + References No definition available. + Details
Name: | cms_EstimatedTimeOfAmortizationOfGainsLosses
Namespace Prefix: | cms_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Prior service cost amortization is established in the year in which the prior service cost first occurred, and is based on the same amortization period for all future years until the prior service costs are fully amortized. + References No definition available. + Details
Name: | cms_EstimatedTimeOfPriorServiceCost
Namespace Prefix: | cms_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Minimum years of participation required before becoming vested. + References No definition available. + Details
Name: | cms_MinimumYearsOfParticipationBeforeVesting
Namespace Prefix: | cms_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of base pay contributed by the Company to the plan for employees. + References No definition available. + Details
Name: | cms_PlanContributionPercentage
Namespace Prefix: | cms_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Participants in the plan include all regular full-time employees covered by the employee health care plan on the day before retirement at age 55 or older with at least ten full years of applicable continuous service. Regular full-time employees who qualify for Pension Plan disability retirement and have 15 years of applicable continuous service may also participate in the plan. + References No definition available. + Details
Name: | cms_RetirementAgeRequirement
Namespace Prefix: | cms_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Participants in the plan include all regular full-time employees covered by the employee health care plan on the day before retirement at age 55 or older with at least ten full years of applicable continuous service. Regular full-time employees who qualify for Pension Plan disability retirement and have 15 years of applicable continuous service may also participate in the plan. + References No definition available. + Details
Name: | cms_RetirementYearsOfService
Namespace Prefix: | cms_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Participants in the plan include all regular full-time employees covered by the employee health care plan on the day before retirement at age 55 or older with at least ten full years of applicable continuous service. Regular full-time employees who qualify for Pension Plan disability retirement and have 15 years of applicable continuous service may also participate in the plan. + References No definition available. + Details
Name: | cms_RetirementYearsOfServiceWithDisability
Namespace Prefix: | cms_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of the cost recognized during the period for a savings plan. + References No definition available. + Details
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- Definition Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=6514294 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=6749293 + 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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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + 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 (l) -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 -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 + Details
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- Definition Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. + 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 (g) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The ultimate trend rate for health care costs. + 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 (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Year the ultimate health care cost trend rate is expected to be reached, in CCYY format. + 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 (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942 + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its pension plans and its non-pension postretirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585 + Details
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