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Variable Interest Entities (Schedule Of Variable Interest Entities) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2016 USD ($)
T.E.S. Filer City [Member] |
Variable Interest Entity [Line Items] |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage | 50.00%
Grayling [Member] |
Variable Interest Entity [Line Items] |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage | 50.00%
Genesee [Member] |
Variable Interest Entity [Line Items] |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage | 50.00%
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount | $ 8
Genesee [Member] | Guarantee of Indebtedness of Others [Member] |
Variable Interest Entity [Line Items] |
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount | $ 3
Craven [Member] |
Variable Interest Entity [Line Items] |
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage | 50.00%

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- Definition The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph b -URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5728-111685 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=64801991&loc=d3e5747-111685 + Details
Name: | us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount
Namespace Prefix: | us-gaap_
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
Name: | us-gaap_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=64801991&loc=SL6759159-111685 + Details
Name: | us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=cms_TESFilerCityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=cms_GraylingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=cms_GeneseeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_GuaranteeOfIndebtednessOfOthersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=cms_CravenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |