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Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Defined Benefit Plan Disclosure [Line Items] |  |
Non-current (liabilities) | $ (872)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent | $ (239)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current (liabilities) | (793)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | (179)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
DB SERP [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current assets (liabilities) | (8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | (8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Non-current (liabilities) | (148)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | (124)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
DB SERP [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current assets (liabilities) | (5)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | (5)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Non-current (liabilities) | (106)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | (88)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current (liabilities) | (113)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |
Non-current assets |  | 95 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
OPEB [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current (liabilities) | (150)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |
Non-current assets |  | 53 us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Pension Plan [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current (liabilities) | (568)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | (109)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Pension Plan [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current (liabilities) | $ (532)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | $ (86)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember

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- Definition The amount for overfunded plans recognized in the balance sheet as a noncurrent asset associated with a defined benefit pension plan or other postretirement defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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- Definition For a classified balance sheet, the amount recognized in balance sheet as a current liability associated with an underfunded defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Current Liabilities -URI http://asc.fasb.org/extlink&oid=6509677 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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- Definition This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2417-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2410-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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