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Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Tax Benefits [Line Items] |  |  |
Interest and penalties | $ 0 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued | $ 0 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued | $ 0 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
IRS audit, adjustments to income tax expense | 0 us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense |  |
Consumers Energy Company [Member] |  |  |
Income Tax Benefits [Line Items] |  |  |
Reduction of income tax expense | 39 cms_ReductionOfIncomeTaxExpense / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Interest and penalties | 0 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 0 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 0 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
IRS audit, adjustments to income tax expense | 0 us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Electric Utility [Member] | Consumers Energy Company [Member] |  |  |
Income Tax Benefits [Line Items] |  |  |
Income tax benefits, to be returned to customers | 209 cms_IncomeTaxBenefitsToBeReturnedToCustomers / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_ElectricUtilityMember |  |
Tax benefit, distribution to customers, term | 5 years |  |
Gas Utility [Member] | Consumers Energy Company [Member] |  |  |
Income Tax Benefits [Line Items] |  |  |
Income tax benefits, to be returned to customers | $ 260 cms_IncomeTaxBenefitsToBeReturnedToCustomers / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_PublicUtilityAxis = cms_GasUtilityMember |  |
Tax benefit, distribution to customers, term | 12 years |  |

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- Definition The total amount of an accelerated return of income tax benefits to customers per regulatory treatment. + References No definition available. + Details
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- Definition The period reduction to income tax expense due to the accelerated return of income tax benefits to customers per regulatory treatment + References No definition available. + Details
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- Definition The period covered related to the accelerated return of income tax benefits to customers per regulatory treatment. + References No definition available. + Details
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- Definition The sum of the amounts of estimated penalties and interest recognized in the period arising from income tax examinations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the 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 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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