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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value $ 12us-gaap_HeldToMaturitySecuritiesFairValue $ 11us-gaap_HeldToMaturitySecuritiesFairValue
Long-term debt, Fair Value 9,562us-gaap_LongTermDebtFairValue [1] 9,285us-gaap_LongTermDebtFairValue [1]
Current notes receivable 103us-gaap_NotesAndLoansReceivableNetCurrent 98us-gaap_NotesAndLoansReceivableNetCurrent
Current portion of long-term debt 521us-gaap_LongTermDebtCurrent 519us-gaap_LongTermDebtCurrent
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value 5,823us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2] 5,749us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2]
Current portion of long-term debt 113us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 124us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value 1,028us-gaap_NotesReceivableFairValueDisclosure
/ dei_LegalEntityAxis
= cms_EnerBankMember		 [3] 995us-gaap_NotesReceivableFairValueDisclosure
/ dei_LegalEntityAxis
= cms_EnerBankMember		 [3]
Current notes receivable 151us-gaap_NotesAndLoansReceivableNetCurrent
/ dei_LegalEntityAxis
= cms_EnerBankMember		 138us-gaap_NotesAndLoansReceivableNetCurrent
/ dei_LegalEntityAxis
= cms_EnerBankMember
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value      
Long-term debt, Fair Value    [1]    [1]
Fair Value, Inputs, Level 1 [Member] | Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value    [2]    [2]
Fair Value, Inputs, Level 1 [Member] | EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value    [3]    [3]
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 12us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 11us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Long-term debt, Fair Value 8,508us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 [1] 8,252us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 [1]
Fair Value, Inputs, Level 2 [Member] | Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value 4,769us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2] 4,716us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2]
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value 1,054us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [1] 1,033us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 [1]
Fair Value, Inputs, Level 3 [Member] | Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value 1,054us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2] 1,033us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2]
Fair Value, Inputs, Level 3 [Member] | EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value 1,028us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= cms_EnerBankMember		 [3] 995us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= cms_EnerBankMember		 [3]
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 12us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember		 11us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Long-term debt, Fair Value 8,664us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember		 [1] 8,535us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember		 [1]
Carrying Amount [Member] | Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value 5,267us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2] 5,278us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 [2]
Carrying Amount [Member] | EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value $ 967us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_EnerBankMember		 [3] $ 938us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_EnerBankMember		 [3]
[1] Includes current portion of long-term debt of $521 million at March 31, 2015 and $519 million at December 31, 2014.
[2] Includes current portion of long-term debt of $113 million at March 31, 2015 and $124 million at December 31, 2014.
[3] Includes current portion of notes receivable of $151 million at March 31, 2015 and $138 million at December 31, 2014.