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Financings And Capitalization (Major Long-Term Debt Transactions) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | $ 1,428 us-gaap_ProceedsFromIssuanceOfLongTermDebt |  | $ 1,025 us-gaap_ProceedsFromIssuanceOfLongTermDebt | $ 1,650 us-gaap_ProceedsFromIssuanceOfLongTermDebt
Debt retirement, principal | 707 us-gaap_RepaymentsOfDebt |  |  |
Loss on extinguishment of debt | (20)us-gaap_GainsLossesOnExtinguishmentOfDebt |  | (4)us-gaap_GainsLossesOnExtinguishmentOfDebt |
CMS Energy [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 550 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  | 275 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | 575 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember
Debt retirement, principal | 530 us-gaap_RepaymentsOfDebt / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Consumers Energy Company [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 878 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 750 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | 1,075 us-gaap_ProceedsFromIssuanceOfLongTermDebt / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Debt retirement, principal | 177 us-gaap_RepaymentsOfDebt / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Senior Notes 3.875% Due March 2024 [Member] | CMS Energy [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 250 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesOneMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Interest rate | 3.875%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SeniorNotesOneMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Debt issuance date | February 2014 |  |  |
Maturity date | March 2024 |  |  |
Senior Notes 4.875% Due March 2044 [Member] | CMS Energy [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 300 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesTwoMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Interest rate | 4.875%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SeniorNotesTwoMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Debt issuance date | February 2014 |  |  |
Maturity date | March 2044 |  |  |
Securitization Bonds 1.334% Due November 2020 [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 124 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_SecuritizationBondsOneMember | [1] |  |
Interest rate | 1.334%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SecuritizationBondsOneMember | [1] |  |
Debt issuance date | July 2014 | [1] |  |
Maturity date | November 2020 | [1] |  |
Securitization Bonds 2.962% Due November 2025 [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 139 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_SecuritizationBondsTwoMember | [1] |  |
Interest rate | 2.962%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SecuritizationBondsTwoMember | [1] |  |
Debt issuance date | July 2014 | [1] |  |
Maturity date | November 2025 | [1] |  |
Securitization Bonds 3.528% Due May 2029 [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 115 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_SecuritizationBondsThreeMember | [1] |  |
Interest rate | 3.528%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SecuritizationBondsThreeMember | [1] |  |
Debt issuance date | July 2014 | [1] |  |
Maturity date | May 2029 | [1] |  |
FMB's 3.125% Due August 2024 [Member] | Consumers Energy Company [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 250 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_FirstMortgageBondsOneMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Interest rate | 3.125%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_FirstMortgageBondsOneMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember | [2] |  |
Debt issuance date | August 2014 |  |  |
Maturity date | August 2024 |  |  |
FMB's 4.350% Due August 2064 [Member] | Consumers Energy Company [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Proceeds from issuance of long-term debt | 250 us-gaap_ProceedsFromIssuanceOfLongTermDebt / us-gaap_DebtInstrumentAxis = cms_FirstMortgageBondsTwoMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Interest rate | 4.35%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_FirstMortgageBondsTwoMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Debt issuance date | August 2014 |  |  |
Maturity date | August 2064 |  |  |
Senior Notes 6.875% Due December 2015 [Member] | CMS Energy [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal | 125 us-gaap_RepaymentsOfDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesThreeMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | [3] |  |
Interest rate | 6.875%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SeniorNotesThreeMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | [3] |  |
Debt retirement date | April 2014 | [3] |  |
Maturity date | December 2015 | [3] |  |
Loss on extinguishment of debt | 13 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesThreeMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Senior Notes 5.500% Due June 2029 [Member] | CMS Energy [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal | 155 us-gaap_RepaymentsOfDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesFourMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Interest rate | 5.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SeniorNotesFourMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
Debt retirement date | June 2014 |  |  |
Maturity date | June 2029 |  |  |
Senior Notes 4.250% Due 2015 [Member] | CMS Energy [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal | 250 us-gaap_RepaymentsOfDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesFiveMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | [4] |  |
Interest rate | 4.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_SeniorNotesFiveMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember | [4] |  |
Debt retirement date | December 2014 | [4] |  |
Maturity date | September 2015 | [4] |  |
Loss on extinguishment of debt | 7 us-gaap_GainsLossesOnExtinguishmentOfDebt / us-gaap_DebtInstrumentAxis = cms_SeniorNotesFiveMember / dei_LegalEntityAxis = us-gaap_ParentCompanyMember |  |  |
FMB's 5.500% Due August 2016 [Member] | Consumers Energy Company [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt retirement, principal | $ 177 us-gaap_RepaymentsOfDebt / us-gaap_DebtInstrumentAxis = cms_FirstMortgageBondsThreeMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Interest rate | 5.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cms_FirstMortgageBondsThreeMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |
Debt retirement date | August 2014 |  |  |
Maturity date | August 2016 |  |  |
[1] | For additional details regarding the Securitization, see Note 3, Regulatory Matters and the “Securitization Bonds” section in this Note.
[2] | The weighted-average interest rate for Consumers’ FMBs was 4.75 percent at December 31, 2014 and 4.90 percent at December 31, 2013.
[3] | CMS Energy retired this debt at a premium and recorded a loss on extinguishment of $13 million in other expense on its consolidated statements of income.
[4] | CMS Energy retired this debt at a premium and recorded a loss on extinguishment of $7 million in other expense on its consolidated statements of income.

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