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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 $ 1,428us-gaap_ProceedsFromIssuanceOfLongTermDebt $ 1,025us-gaap_ProceedsFromIssuanceOfLongTermDebt $ 1,650us-gaap_ProceedsFromIssuanceOfLongTermDebt
Debt retirement, principal 707us-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 550us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		 275us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		 575us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Debt retirement, principal 530us-gaap_RepaymentsOfDebt
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		    
Consumers Energy Company [Member]      
Debt Instrument [Line Items]      
Proceeds from issuance of long-term debt 878us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 750us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 1,075us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
Debt retirement, principal 177us-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 250us-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 300us-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 124us-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 139us-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 115us-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 250us-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 250us-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 125us-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 13us-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 155us-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 250us-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 7us-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 $ 177us-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.