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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	$ 1,956us-gaap_RegulatoryAssetsNoncurrent			$ 1,530us-gaap_RegulatoryAssetsNoncurrent
Consumers Energy Company [Member]
Loss Contingencies [Line Items]
Regulatory assets	1,956us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember			1,530us-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	8cms_DemandForPaymentByUsepa / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Increase in liability due to change in estimates			15us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Cumulative environmental charge	245cms_CumulativeEnvironmentalCharge / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Accrual for environmental loss contingencies	62us-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	80us-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	3us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_CerclaLiabilityMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Remediation and other response activity costs, minimum	3us-gaap_LossContingencyRangeOfPossibleLossMinimum / us-gaap_EnvironmentalRemediationSiteAxis = cms_CerclaLiabilityMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Remediation and other response activity costs. maximum	9us-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	115us-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	131us-gaap_AccrualForEnvironmentalLossContingenciesGross / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Number of former MGPs	23cms_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			7.7cms_LitigationSettlementEnvironmentalMitigationsProjectsRequiredInvestment / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Litigation settlement, gross			2.75us-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	4us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember
Remediation and other response activity costs, minimum	4us-gaap_LossContingencyRangeOfPossibleLossMinimum / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember
Remediation and other response activity costs. maximum	6us-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	14cms_NumberOfBoilersAllegedToExceedEmissionLimits / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember
Alleged number of facilities in violation	3cms_AllegedNumberOfFacilitiesInViolation / us-gaap_EnvironmentalRemediationSiteAxis = cms_EpaNovMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember
Number of projects affected by alleged violations	10cms_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	1us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_GasUtilityMember
Remediation and other response activity costs. maximum	3us-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	23cms_NumberOfFormerManufacturedGasPlants / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_ManufacturedGasPlantMember
Regulatory assets	147us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_RegulatoryAssetAxis = cms_ManufacturedGasPlantMember	[1]		148us-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	$ 142cms_ForeignGovernmentTaxClaimOnSale / us-gaap_IncomeTaxAuthorityNameAxis = cms_EquatorialGuineaTaxAuthorityMember
Gas Index Price Reporting [Member]
Loss Contingencies [Line Items]
Number of lawsuits	5cms_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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Alleged number of facilities in violation

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CCR Rule, Compliance Term

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Environmental remediation permit renewal term

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Litigation settlement, Environmental mitigation projects, required investment

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Number of boilers alleged to exceed emission limits

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Number of Former Manufactured Gas Plants

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Number of projects affected by alleged violations

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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