XML 49 R89.htm IDEA: XBRL DOCUMENT v2.4.1.9
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 $ 32us-gaap_PensionAndOtherPostretirementBenefitContributions $ 229us-gaap_PensionAndOtherPostretirementBenefitContributions $ 72us-gaap_PensionAndOtherPostretirementBenefitContributions
Union employees percentage 41.00%cms_UnionMembershipByTotalEmployeesPercentage    
Consumers Energy Company [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions 29us-gaap_PensionAndOtherPostretirementBenefitContributions
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
222us-gaap_PensionAndOtherPostretirementBenefitContributions
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
68us-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 1,979us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
1,964us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
1,727us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Estimated time of amortization of gains losses 10 years 10 years 11 years
Postretirement benefits contributions   150us-gaap_PensionAndOtherPostretirementBenefitContributions
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
[1]  
Actuarial loss 458us-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   147us-gaap_PensionAndOtherPostretirementBenefitContributions
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[1]  
OPEB [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Trust assets 1,265us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1,218us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1,047us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Retirement age requirement 55cms_RetirementAgeRequirement
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
55cms_RetirementAgeRequirement
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
55cms_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 25us-gaap_PensionAndOtherPostretirementBenefitContributions
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
[2] 72us-gaap_PensionAndOtherPostretirementBenefitContributions
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
[2]  
Estimated future employer contributions 29us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Actuarial loss 230us-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 1,186us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
1,141us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
978us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
Retirement age requirement 55cms_RetirementAgeRequirement
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
55cms_RetirementAgeRequirement
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
55cms_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 25us-gaap_PensionAndOtherPostretirementBenefitContributions
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2] 71us-gaap_PensionAndOtherPostretirementBenefitContributions
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2]  
Estimated future employer contributions 29us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
   
Actuarial loss 223us-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 13us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_DefinedCompanyContributionPlanMember
10us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_DefinedCompanyContributionPlanMember
8us-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 13us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_DefinedCompanyContributionPlanMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
10us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_DefinedCompanyContributionPlanMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
8us-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 2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedContributionPlanNameAxis
= cms_SupplementalEmployeeRetirementPlanDefinedContributionMember
1us-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 2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedContributionPlanNameAxis
= cms_SupplementalEmployeeRetirementPlanDefinedContributionMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
1us-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 18cms_SavingsPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_Plan401KMember
17cms_SavingsPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_Plan401KMember
16cms_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 18cms_SavingsPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_Plan401KMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
17cms_SavingsPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_Plan401KMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
16cms_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 1us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_SupplementalEmployeeRetirementPlanDefinedContributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
1us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_SupplementalEmployeeRetirementPlanDefinedContributionMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
1us-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 $ 1us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_SupplementalEmployeeRetirementPlanDefinedContributionMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
$ 1us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedContributionPlanNameAxis
= cms_SupplementalEmployeeRetirementPlanDefinedContributionMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
$ 1us-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.