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Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Pension And DB SERP [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | $ 1,012 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember | $ 625 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember
Regulatory assets (liabilities), Prior service cost (credit) | 7 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember | 9 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember
Regulatory assets (liabilities) | 1,019 us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember | 634 us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember
AOCI, Net loss (gain) | 99 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember | 69 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember
AOCI, Prior service cost (credit) | 1 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember |
Total amounts not yet recognized as component of net periodic benefit cost | 1,119 cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember | 703 cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember
Pension And DB SERP [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | 1,012 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 625 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Regulatory assets (liabilities), Prior service cost (credit) | 7 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 9 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Regulatory assets (liabilities) | 1,019 us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 634 us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
AOCI, Net loss (gain) | 39 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 25 us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Total amounts not yet recognized as component of net periodic benefit cost | 1,058 cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 659 cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cms_PensionAndDBSERPMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
OPEB [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | 419 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 184 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Regulatory assets (liabilities), Prior service cost (credit) | (243)cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (282)cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Regulatory assets (liabilities) | 176 us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (98)us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
AOCI, Net loss (gain) | (18)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (26)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
AOCI, Prior service cost (credit) | (8)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (10)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Total amounts not yet recognized as component of net periodic benefit cost | 150 cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | (134)cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
OPEB [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | 419 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 184 cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetGainsLossesBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Regulatory assets (liabilities), Prior service cost (credit) | (243)cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | (282)cms_PensionAndOtherPostretirementBenefitPlansRegulatoryAssetsNetPriorServiceCostCreditBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Regulatory assets (liabilities) | 176 us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | (98)us-gaap_NetRegulatoryAssets / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Total amounts not yet recognized as component of net periodic benefit cost | $ 176 cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | $ (98)cms_TotalAmountsNotYetRecognizedAsComponentOfNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember

X
- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in regulatory assets as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References No definition available. + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References No definition available. + Details
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- Definition Total amount of regulatory assets and AOCI that have not been recognized as a component of net periodic cost. + References No definition available. + Details
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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=6521920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=6521884 + Details
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- Definition The net amount of all regulatory assets less all regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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