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Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Jan. 31, 2015 | Mar. 31, 2015 | Dec. 31, 2014
Financial Instruments [Line Items] |  |  |
Portion of long-term debt supported by third-party credit enhancements |  | $ 103 cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement | $ 103 cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement
Consumers Energy Company [Member] |  |  |
Financial Instruments [Line Items] |  |  |
Portion of long-term debt supported by third-party credit enhancements |  | 103 cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 103 cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Gain on CMS Energy common stock | 9 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
DB SERP [Member] |  |  |
Financial Instruments [Line Items] |  |  |
Company contributions |  | 25 us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |
DB SERP [Member] | Consumers Energy Company [Member] |  |  |
Financial Instruments [Line Items] |  |  |
Company contributions |  | $ 17 us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |

X
- Definition Disclosure of the amount of the entity's issued liability supported by a third-party credit enhancement. + References No definition available. + Details
Name: | cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | cms_FinancialInstrumentsLineItems
Namespace Prefix: | cms_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The increase in the fair value of plan assets from contributions made by the employer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=cms_ConsumersEnergyCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |