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Financial Instruments (Narrative) (Details) $ in Millions | Dec. 31, 2019 USD ($)
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Portion of long-term debt supported by third-party credit enhancements | $ 35
Consumers Energy Company |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Portion of long-term debt supported by third-party credit enhancements | $ 35

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

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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