XML 57 R71.htm IDEA: XBRL DOCUMENT v2.4.1.9
Financial Instruments (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Financial Instruments [Line Items]      
Portion of long-term debt supported by third-party credit enhancements $ 103cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement   $ 103cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement
Consumers Energy Company [Member]      
Financial Instruments [Line Items]      
Portion of long-term debt supported by third-party credit enhancements 103cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		   103cms_DebtInstrumentSupportedByThirdPartyCreditEnhancement
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember
Gain on CMS Energy common stock $ 4us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember		 $ 5us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
/ dei_LegalEntityAxis
= cms_ConsumersEnergyCompanyMember