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Regulatory Matters (Narrative) (Details) (USD $) | 12 Months Ended |
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2014 | Mar. 31, 2013 | Nov. 30, 2014
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Proceeds from government grant |  | $ 69,000,000 cms_ProceedsFromGovernmentGrant |  |  |  |
Accrued Power Supply | 27,000,000 us-gaap_DeferredFuelCost |  |  |  |  |
Long-term debt | 8,016,000,000 us-gaap_LongTermDebtNoncurrent | 7,101,000,000 us-gaap_LongTermDebtNoncurrent |  |  |  |
Accrued rate refunds | 6,000,000 cms_AccruedRateRefunds | 12,000,000 cms_AccruedRateRefunds |  |  |  |
Cost of gas sold | 1,493,000,000 us-gaap_CostOfNaturalGasPurchases | 1,228,000,000 us-gaap_CostOfNaturalGasPurchases | 1,150,000,000 us-gaap_CostOfNaturalGasPurchases |  |  |
Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Income tax benefits returned to customers | 64,000,000 cms_IncomeTaxBenefitsReturnedToCustomers / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |  |
Reduction of income tax expense | 39,000,000 cms_ReductionOfIncomeTaxExpense / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |  |
Proceeds from government grant |  | 69,000,000 cms_ProceedsFromGovernmentGrant / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Accrued Power Supply | 27,000,000 us-gaap_DeferredFuelCost / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |  |
Energy optimization incentive authorized for exceeding savings targets |  |  |  |  |  | 18,000,000 cms_EnergyOptimizationIncentiveAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Energy optimization incentive requested for exceeding savings targets | 17,000,000 cms_RequestedEnergyOptimizationIncentive / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |  |
Long-term debt | 5,154,000,000 us-gaap_LongTermDebtNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 4,579,000,000 us-gaap_LongTermDebtNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Recorded liability | 2,162,000,000 us-gaap_RegulatoryLiabilities / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 2,282,000,000 us-gaap_RegulatoryLiabilities / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Number of units planned to be retired | 10 cms_NumberOfUnitsPlannedToBeRetired / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |  |
Accrued rate refunds | 6,000,000 cms_AccruedRateRefunds / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 12,000,000 cms_AccruedRateRefunds / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Cost of gas sold | 1,375,000,000 us-gaap_CostOfNaturalGasPurchases / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1,187,000,000 us-gaap_CostOfNaturalGasPurchases / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1,110,000,000 us-gaap_CostOfNaturalGasPurchases / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Coal-Fueled Electric Generation [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Number of units planned to be retired | 7 cms_NumberOfUnitsPlannedToBeRetired / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_CoalFueledElectricGenerationMember |  |  |  |  |
Gas-Fueled Electric Generation [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Number of units planned to be retired | 3 cms_NumberOfUnitsPlannedToBeRetired / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_GasFueledElectricGenerationMember |  |  |  |  |
Electric Utility [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Income tax benefits, to be returned to customers | 209,000,000 cms_IncomeTaxBenefitsToBeReturnedToCustomers / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |  |
Tax benefit, distribution to customers, term | 5 years |  |  |  |  |
Gas Utility [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Income tax benefits, to be returned to customers | 260,000,000 cms_IncomeTaxBenefitsToBeReturnedToCustomers / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_GasUtilityMember |  |  |  |  |
Tax benefit, distribution to customers, term | 12 years |  |  |  |  |
Gas Cost Recover (GCR) [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Over (under) recovery requested |  |  |  | (84,000,000)cms_NetOverUnderRecoveryOfExpenseIncludingInterestRequested / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_GasCostRecoveryMember |  |
Over (under) recovery authorized by the MPSC |  |  |  |  | (22,000,000)cms_NetOverUnderRecoveryOfExpenseIncludingInterestAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_GasCostRecoveryMember |
Cost of gas sold |  |  |  | 900,000,000 us-gaap_CostOfNaturalGasPurchases / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_GasCostRecoveryMember | 900,000,000 us-gaap_CostOfNaturalGasPurchases / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_GasCostRecoveryMember |
Deferred gas costs | 27,000,000 us-gaap_DeferredGasCost / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_GasCostRecoveryMember |  |  |  |  |
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Over (under) recovery requested |  | 10,000,000 cms_NetOverUnderRecoveryOfExpenseIncludingInterestRequested / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_PowerSupplyCostRecoveryMember |  |  |  |
Accrued rate refunds | 6,000,000 cms_AccruedRateRefunds / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_PowerSupplyCostRecoveryMember |  |  |  |  |
PSCR Cost of Power Sold |  | 1,900,000,000 us-gaap_CostOfGoodsSoldElectric / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_PowerSupplyCostRecoveryMember | 1,900,000,000 us-gaap_CostOfGoodsSoldElectric / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_PowerSupplyCostRecoveryMember |  |  |
Over (under) recovery authorized by the MPSC |  |  | (18,000,000)cms_NetOverUnderRecoveryOfExpenseIncludingInterestAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_PowerSupplyCostRecoveryMember |  |  |
Electric Energy Optimization Plan [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Percent of savings target achieved | 135.00%cms_PercentOfSavingsTargetAchieved / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_ElectricEnergyOptimizationPlanMember |  |  |  |  |
Gas Energy Optimization Plan [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Percent of savings target achieved | 129.00%cms_PercentOfSavingsTargetAchieved / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_GasEnergyOptimizationPlanMember |  |  |  |  |
Cancelled Coal-Fueled Plant Costs [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period | 3 years |  |  |  |  |
Authorized Recovery |  |  | 14,000,000 cms_AuthorizedRecovery / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilitiesRegulatoryProceedingAxis = cms_CancelledCoalFueledPlantCostsMember |  |  |
Major Maintenance [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period | 6 months |  |  |  |  |
Authorized Recovery |  |  |  |  |  | 10,000,000 cms_AuthorizedRecovery / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_MajorMaintenanceMember
Coal Fueled Electric Generating Units [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Power generation of cancelled plant |  |  | 830 cms_PowerGenerationOfCancelledPlant / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_CoalFueledElectricGeneratingUnitsMember |  |  |
Manufactured Gas Plant [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period | 10 years |  |  |  |  |
Number of former MGPs | 23 cms_NumberOfFormerManufacturedGasPlants / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_ManufacturedGasPlantMember |  |  |  |  |
Gas Storage Inventory Adjustments [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized recovery, collection period | 5 years |  |  |  |  |
Gas Revenue Decoupling Mechanism [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Authorized Recovery |  | 17,000,000 cms_AuthorizedRecovery / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_GasRevenueDecouplingMechanismMember |  |  |  |
Renewable Energy Grant [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Proceeds from government grant |  | $ 69,000,000 cms_ProceedsFromGovernmentGrant / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryLiabilityAxis = cms_RenewableEnergyGrantMember |  |  |  |

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