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Retirement Benefits (Schedule Of Net Loss And Prior Service Cost (Credit) That Will Be Amortized In 2015) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014
Pension Plan [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Regulatory asset | $ 89 cms_DefinedBenefitPlanAmountToBeAmortizedFromRegulatoryAssetsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
AOCI | 3 us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Consumers Energy Company [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Regulatory asset | 89 cms_DefinedBenefitPlanAmountToBeAmortizedFromRegulatoryAssetsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Regulatory asset | (18)cms_DefinedBenefitPlanAmountToBeAmortizedFromRegulatoryAssetsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
AOCI | (2)us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
OPEB [Member] | Consumers Energy Company [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Regulatory asset | $ (18)cms_DefinedBenefitPlanAmountToBeAmortizedFromRegulatoryAssetsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember

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- Definition Defined benefit plan, amount to be amortized from (to) regulatory assets in next fiscal year. + References No definition available. + Details
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Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation). + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
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- Details
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Data Type: | na
Balance Type: |
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