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Income Taxes (Reconciliation Of Beginning And Ending Uncertain Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Balance at beginning of period | $ 4 us-gaap_UnrecognizedTaxBenefits | $ 1 us-gaap_UnrecognizedTaxBenefits | $ 4 us-gaap_UnrecognizedTaxBenefits
Additions for current year tax positions | 2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions |  |
Additions for prior year tax positions | 1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 3 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Reductions for prior year tax positions | (2)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions |  | (4)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions
Balance at end of period | 5 us-gaap_UnrecognizedTaxBenefits | 4 us-gaap_UnrecognizedTaxBenefits | 1 us-gaap_UnrecognizedTaxBenefits
Consumers Energy Company [Member] |  |  |
Balance at beginning of period | 4 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 4 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Additions for current year tax positions | 2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Additions for prior year tax positions | 1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 3 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Reductions for prior year tax positions | (2)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | (4)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Balance at end of period | $ 5 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | $ 4 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | $ 1 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember

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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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