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Financial Instruments (Narrative) (Details) - USD ($) $ in Millions | Jun. 30, 2017 | Dec. 31, 2016
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Financial Instruments [Line Items] |  |
Portion of long-term debt supported by third-party credit enhancements | $ 103 | $ 103
Consumers Energy Company [Member] |  |
Financial Instruments [Line Items] |  |
Portion of long-term debt supported by third-party credit enhancements | $ 103 | $ 103

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

X
- Definition Financial Instruments [Line Items] + References No definition available. + Details
Name: | cms_FinancialInstrumentsLineItems
Namespace Prefix: | cms_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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