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Contingencies And Commitments (Contingencies And Commitments) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014
Loss Contingencies [Line Items] |  |
Regulatory assets | $ 1,932 us-gaap_RegulatoryAssetsNoncurrent | $ 1,956 us-gaap_RegulatoryAssetsNoncurrent
Consumers Energy Company [Member] |  |
Loss Contingencies [Line Items] |  |
Regulatory assets | 1,932 us-gaap_RegulatoryAssetsNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1,956 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 |
Cumulative environmental charge | 246 cms_CumulativeEnvironmentalCharge / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember |
Accrual for environmental loss contingencies | 61 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 | 78 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 |
Regulatory assets | 145 us-gaap_RegulatoryAssetsNoncurrent / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |
Authorized recovery, collection period | 10 years |
Accrual for environmental loss contingencies, inflation rate | 2.50%cms_AccrualForEnvironmentalLossContingenciesInflationRate / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / 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 | 5 us-gaap_LossContingencyRangeOfPossibleLossMaximum / us-gaap_EnvironmentalRemediationSiteAxis = cms_NrepaMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / 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 |
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 |

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