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Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value $ 11us-gaap_HeldToMaturitySecuritiesFairValue $ 10us-gaap_HeldToMaturitySecuritiesFairValue
Long-term debt, Fair Value 9,285us-gaap_LongTermDebtFairValue [1] 8,368us-gaap_LongTermDebtFairValue [1]
Current notes receivable 98us-gaap_NotesAndLoansReceivableNetCurrent 63us-gaap_NotesAndLoansReceivableNetCurrent
Current portion of long-term debt 519us-gaap_LongTermDebtCurrent 541us-gaap_LongTermDebtCurrent
Consumers Energy Company [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, Fair Value 5,749us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2] 4,940us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2]
Current notes receivable   14us-gaap_NotesAndLoansReceivableNetCurrent
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
Current portion of long-term debt 124us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
43us-gaap_LongTermDebtCurrent
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
EnerBank [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Notes receivable, Fair Value 995us-gaap_NotesReceivableFairValueDisclosure
/ dei_LegalEntityAxis
= cms_EnerBankMember
[3] 724us-gaap_NotesReceivableFairValueDisclosure
/ dei_LegalEntityAxis
= cms_EnerBankMember
[3]
Current notes receivable 138us-gaap_NotesAndLoansReceivableNetCurrent
/ dei_LegalEntityAxis
= cms_EnerBankMember
48us-gaap_NotesAndLoansReceivableNetCurrent
/ dei_LegalEntityAxis
= cms_EnerBankMember
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Securities held to maturity - Fair Value 11us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
10us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Long-term debt, Fair Value 8,252us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
[1] 7,406us-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 4,716us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2] 3,978us-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 1,033us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
[1] 962us-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 1,033us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2] 962us-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 995us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= cms_EnerBankMember
[3] 724us-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 11us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
10us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Long-term debt, Fair Value 8,535us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
[1] 7,642us-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 5,278us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
[2] 4,622us-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 $ 938us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_EnerBankMember
[3] $ 683us-gaap_NotesReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= cms_EnerBankMember
[3]
[1] Includes current portion of long-term debt of $519 million at December 31, 2014 and $541 million at December 31, 2013.
[2] Includes current portion of long-term debt of $124 million at December 31, 2014 and $43 million at December 31, 2013.
[3] Includes current portion of notes receivable of $138 million at December 31, 2014 and $48 million at December 31, 2013.