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Financings And Capitalization (Narrative) (Details) (USD $) | 12 Months Ended | 24 Months Ended |
--- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2013
Financing And Capitalization [Line Items] |  |  |  |  |
Limitation on payment of stock dividends | $ 3,700,000,000 cms_AmountAvailableForDividendDistribution |  | $ 3,700,000,000 cms_AmountAvailableForDividendDistribution |  |
Common stock dividends from Consumers | 457,000,000 us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries |  |  |  |
Common stock, shares authorized | 350,000,000 us-gaap_CommonStockSharesAuthorized |  | 350,000,000 us-gaap_CommonStockSharesAuthorized |  | 350,000,000 us-gaap_CommonStockSharesAuthorized
Par value of Common Stock | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  | $ 0.01 us-gaap_CommonStockParOrStatedValuePerShare |  |
Shares of Preferred Stock authorized | 10,000,000 us-gaap_PreferredStockSharesAuthorized |  | 10,000,000 us-gaap_PreferredStockSharesAuthorized |  |
Par value of Preferred Stock | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  | $ 0.01 us-gaap_PreferredStockParOrStatedValuePerShare |  |
Consumers Energy Company [Member] |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |
Maximum allowed short term securities outstanding under FERC Authorization | 800,000,000 cms_MaximumAllowedShortTermSecuritiesOutstanding / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 800,000,000 cms_MaximumAllowedShortTermSecuritiesOutstanding / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Maximum allowed long-term securites outstanding under FERC Authorization | 1,900,000,000 cms_MaximumAllowedLongTermSecuritesOutstanding / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 1,900,000,000 cms_MaximumAllowedLongTermSecuritesOutstanding / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Long-term securities, remaining availability under FERC Authorization | 1,400,000,000 cms_LongTermSecuritiesRemainingAvailability / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 1,400,000,000 cms_LongTermSecuritiesRemainingAvailability / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Unrestricted retained earnings | 768,000,000 us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 768,000,000 us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApproval / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Common stock, shares authorized | 125,000,000 us-gaap_CommonStockSharesAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 125,000,000 us-gaap_CommonStockSharesAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 125,000,000 us-gaap_CommonStockSharesAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Shares of Preferred Stock authorized | 7,500,000 us-gaap_PreferredStockSharesAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 7,500,000 us-gaap_PreferredStockSharesAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 7,500,000 us-gaap_PreferredStockSharesAuthorized / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Par value of Preferred Stock | $ 100 us-gaap_PreferredStockParOrStatedValuePerShare / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | $ 100 us-gaap_PreferredStockParOrStatedValuePerShare / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 100 us-gaap_PreferredStockParOrStatedValuePerShare / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember
Consumers Energy Company [Member] | Commercial Paper [Member] |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |
Weighted average annual interest rate | 0.49%us-gaap_ShortTermDebtWeightedAverageInterestRate / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_CommercialPaperMember |  | 0.49%us-gaap_ShortTermDebtWeightedAverageInterestRate / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_CommercialPaperMember |  |
Short-term debt, authorized borrowings | 500,000,000 cms_ShortTermDebtAuthorizedBorrowings / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_CommercialPaperMember |  |  |  |
Short-term borrowings outstanding | 60,000,000 us-gaap_ShortTermBorrowings / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_CommercialPaperMember |  | 60,000,000 us-gaap_ShortTermBorrowings / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_ShortTermDebtTypeAxis = us-gaap_CommercialPaperMember |  |
Short Term Secured Borrowing Accounts Receivable Sales Program [Member] | Consumers Energy Company [Member] |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |
Amount of accounts receivable eligible for transfer | 250,000,000 cms_AccountsReceivalbeSalesProgramMaximumBorrowingCapacity / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 250,000,000 cms_AccountsReceivalbeSalesProgramMaximumBorrowingCapacity / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Average short-term borrowings | 11,000,000 us-gaap_ShorttermDebtAverageOutstandingAmount / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |  |  |
Weighted average annual interest rate | 0.85%us-gaap_ShortTermDebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 0.85%us-gaap_ShortTermDebtWeightedAverageInterestRate / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Short-term borrowings outstanding | 0 us-gaap_ShortTermBorrowings / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  | 0 us-gaap_ShortTermBorrowings / us-gaap_DebtInstrumentAxis = cms_ShortTermSecuredBorrowingAccountsReceivableSalesProgramMember / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember |  |
Continuous Equity Program [Member] |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |
Aggregate sales price of an equity offering program |  |  | 50,000,000 cms_StockOfferingProgramMaximumValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = cms_ContinuousEquityProgramMember |  |
Revolving Credit Facilities December 20, 2018 [Member] |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |
Amount of Facility | 550,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_LineOfCreditFacilityAxis = cms_RevolvingCreditFacilitiesDecemberTwentyTwoThousandEighteenMember | [1] | 550,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_LineOfCreditFacilityAxis = cms_RevolvingCreditFacilitiesDecemberTwentyTwoThousandEighteenMember | [1] |
Revolving Credit Facilities December 20, 2018 [Member] | Consumers Energy Company [Member] |  |  |  |  |
Financing And Capitalization [Line Items] |  |  |  |  |
Amount of Facility | $ 650,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_LineOfCreditFacilityAxis = cms_RevolvingCreditFacilitiesDecemberTwentyTwoThousandEighteenMember | [2] | $ 650,000,000 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / dei_LegalEntityAxis = cms_ConsumersEnergyCompanyMember / us-gaap_LineOfCreditFacilityAxis = cms_RevolvingCreditFacilitiesDecemberTwentyTwoThousandEighteenMember | [2] |
[1] | Obligations under this facility are secured by Consumers common stock.
[2] | Obligations under this facility are secured by FMBs of Consumers.

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