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Contingencies And Commitments (Expected Remediation Cost By Year) (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2015
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Manufactured Gas Plant [Member] | Consumers Energy Company [Member] |
Site Contingency [Line Items] |
Undiscounted amount due within one year | $ 11 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInRemainderOfFiscalYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Undiscounted amount due within two year | 12 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInSecondYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Undiscounted amount due within third year | 13 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInThirdYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Undiscounted amount due within fourth year | 11 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInFourthYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Undiscounted amount due within five year | 14 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInFifthYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_ManufacturedGasPlantMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Bay Harbor [Member] |
Site Contingency [Line Items] |
Undiscounted amount due within one year | 7 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInRemainderOfFiscalYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Undiscounted amount due within two year | 6 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInSecondYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Undiscounted amount due within third year | 5 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInThirdYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Undiscounted amount due within fourth year | 5 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInFourthYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember
Undiscounted amount due within five year | $ 5 us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInFifthYear / us-gaap_EnvironmentalRemediationSiteAxis = cms_BayHarborMember

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- Definition Undiscounted amount of the accrual for environmental loss contingencies expected to be paid in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section Y -Paragraph Question 1 + Details
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- Definition Undiscounted amount of the accrual for environmental loss contingencies expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section Y -Paragraph Question 1 + Details
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- Definition Undiscounted amount of the accrual for environmental loss contingencies expected to be paid in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References No definition available. + Details
Name: | us-gaap_AccrualForEnvironmentalLossContingenciesUndiscountedDueInRemainderOfFiscalYear
Namespace Prefix: | us-gaap_
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- Definition Undiscounted amount of the accrual for environmental loss contingencies expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section Y -Paragraph Question 1 + Details
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- Definition Undiscounted amount of the accrual for environmental loss contingencies expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q1) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section Y -Paragraph Question 1 + Details
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- Details
Name: | us-gaap_SiteContingencyLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=cms_BayHarborMember
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Period Type: |

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- Details
Name: | us-gaap_EnvironmentalRemediationSiteAxis=cms_ManufacturedGasPlantMember
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Balance Type: |
Period Type: |