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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
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Securities held to maturity - Fair Value | $ 12 us-gaap_HeldToMaturitySecuritiesFairValue |  | $ 11 us-gaap_HeldToMaturitySecuritiesFairValue |
Long-term debt, Fair Value | 9,562 us-gaap_LongTermDebtFairValue | [1] | 9,285 us-gaap_LongTermDebtFairValue | [1]
Current notes receivable | 103 us-gaap_NotesAndLoansReceivableNetCurrent |  | 98 us-gaap_NotesAndLoansReceivableNetCurrent |
Current portion of long-term debt | 521 us-gaap_LongTermDebtCurrent |  | 519 us-gaap_LongTermDebtCurrent |
Consumers Energy Company [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Long-term debt, Fair Value | 5,823 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] | 5,749 us-gaap_LongTermDebtFairValue / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2]
Current portion of long-term debt | 113 us-gaap_LongTermDebtCurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 124 us-gaap_LongTermDebtCurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |
EnerBank [Member] |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Notes receivable, Fair Value | 1,028 us-gaap_NotesReceivableFairValueDisclosure / dei_LegalEntityAxis = cms_EnerBankMember | [3] | 995 us-gaap_NotesReceivableFairValueDisclosure / dei_LegalEntityAxis = cms_EnerBankMember | [3]
Current notes receivable | 151 us-gaap_NotesAndLoansReceivableNetCurrent / dei_LegalEntityAxis = cms_EnerBankMember |  | 138 us-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 | 12 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |  | 11 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Long-term debt, Fair Value | 8,508 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | [1] | 8,252 us-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 | 4,769 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] | 4,716 us-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 | 1,054 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | [1] | 1,033 us-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 | 1,054 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] | 1,033 us-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 | 1,028 us-gaap_NotesReceivableFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / dei_LegalEntityAxis = cms_EnerBankMember | [3] | 995 us-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 | 12 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |  | 11 us-gaap_HeldToMaturitySecuritiesFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Long-term debt, Fair Value | 8,664 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | [1] | 8,535 us-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 | 5,267 us-gaap_LongTermDebtFairValue / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] | 5,278 us-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 | $ 967 us-gaap_NotesReceivableFairValueDisclosure / us-gaap_FairValueByMeasurementBasisAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember / dei_LegalEntityAxis = cms_EnerBankMember | [3] | $ 938 us-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.

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- Definition Fair value of investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 + Details
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- Definition Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19,20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Article 5 + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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- Definition An amount representing an agreement for an unconditional promise by the maker to pay the Company (holder) a definite sum of money within one year from the balance sheet date (or the normal operating cycle, whichever is longer), net of any write-downs taken for collection uncertainty on the part of the holder. Such amount may include accrued interest receivable in accordance with the terms of the debt. The debt also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. This amount does not include amounts related to receivables held-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4531-111522 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765 + Details
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- Definition Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph b -Article 5 + Details
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