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Contingencies And Commitments (Contingencies And Commitments) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Dec. 31, 2014 | Sep. 30, 2014 | Dec. 31, 2013
Loss Contingencies [Line Items] |  |  |  |  |
CCR Rule, Compliance term | 3 years |  |  |  |
Regulatory assets | $ 1,956 us-gaap_RegulatoryAssetsNoncurrent |  |  | $ 1,530 us-gaap_RegulatoryAssetsNoncurrent |
Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Regulatory assets | 1,956 us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  | 1,530 us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |
Bay Harbor [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Environmental remediation permit renewal term | 5 years |  |  |  |
Demand for payment by USEPA | 8 cms_DemandForPaymentByUsepa / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |  |  |
Increase in liability due to change in estimates |  |  | 15 us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |
Cumulative environmental charge | 245 cms_CumulativeEnvironmentalCharge / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |  |  |
Accrual for environmental loss contingencies | 62 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |  |  |
Discounted projected costs rate | 4.34%us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |  |  |
Remaining undiscounted obligation amount | 80 us-gaap_AccrualForEnvironmentalLossContingenciesGross / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |  |  |
Accrual for environmental loss contingencies, inflation rate | 1.00%cms_AccrualForEnvironmentalLossContingenciesInflationRate / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |  |  |  |
CERCLA Liability [Member] | Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Accrual for environmental loss contingencies | 3 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_CerclaLiabilityMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Remediation and other response activity costs, minimum | 3 us-gaap_LossContingencyRangeOfPossibleLossMinimum / us-gaap_EnvironmentalRemediationSiteAxis = cms_CerclaLiabilityMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Remediation and other response activity costs. maximum | 9 us-gaap_LossContingencyRangeOfPossibleLossMaximum / us-gaap_EnvironmentalRemediationSiteAxis = cms_CerclaLiabilityMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Manufactured Gas Plant [Member] | Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Accrual for environmental loss contingencies | 115 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Discounted projected costs rate | 2.57%us-gaap_AccrualForEnvironmentalLossContingenciesDiscountRate / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Remaining undiscounted obligation amount | 131 us-gaap_AccrualForEnvironmentalLossContingenciesGross / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Number of former MGPs | 23 cms_NumberOfFormerManufacturedGasPlants / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Accrual for environmental loss contingencies, inflation rate | 2.50%cms_AccrualForEnvironmentalLossContingenciesInflationRate / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
EPA NOV [Member] | Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Environmental mitigation projects, required investment |  |  | 7.7 cms_LitigationSettlementEnvironmentalMitigationsProjectsRequiredInvestment / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Litigation settlement, gross |  |  | 2.75 us-gaap_LitigationSettlementAmount / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Electric Utility [Member] | NREPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Accrual for environmental loss contingencies | 4 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |
Remediation and other response activity costs, minimum | 4 us-gaap_LossContingencyRangeOfPossibleLossMinimum / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |
Remediation and other response activity costs. maximum | 6 us-gaap_LossContingencyRangeOfPossibleLossMaximum / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |
Electric Utility [Member] | EPA NOV [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Number of boilers alleged to exceed emission limits | 14 cms_NumberOfBoilersAllegedToExceedEmissionLimits / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |
Alleged number of facilities in violation | 3 cms_AllegedNumberOfFacilitiesInViolation / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |
Number of projects affected by alleged violations | 10 cms_NumberOfProjectsAffectedByAllegedViolations / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |  |  |
Gas Utility [Member] | NREPA [Member] | Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Accrual for environmental loss contingencies | 1 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_GasUtilityMember |  |  |  |
Remediation and other response activity costs. maximum | 3 us-gaap_LossContingencyRangeOfPossibleLossMaximum / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_GasUtilityMember |  |  |  |
Manufactured Gas Plant [Member] | Consumers Energy Company [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Number of former MGPs | 23 cms_NumberOfFormerManufacturedGasPlants / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_ManufacturedGasPlantMember |  |  |  |
Regulatory assets | 147 us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_ManufacturedGasPlantMember | [1] |  | 148 us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_ManufacturedGasPlantMember | [1]
Authorized recovery, collection period | 10 years |  |  |  |
Equatorial Guinea Tax Claim [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Foreign government tax claim on sale | $ 142 cms_ForeignGovernmentTaxClaimOnSale / us-gaap_IncomeTaxAuthorityNameAxis = cms_EquatorialGuineaTaxAuthorityMember |  |  |  |
Gas Index Price Reporting [Member] |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Number of lawsuits | 5 cms_LossContingencyNumberOfLawsuits / us-gaap_LitigationCaseAxis = cms_GasIndexPriceReportingMember |  |  |  |
[1] | These regulatory assets represent incurred costs for which the MPSC has provided, or Consumers expects, recovery without a return on investment.

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