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Employee Benefit Plans Other Employee Matters (Details)
12 Months Ended
Dec. 31, 2014
Concentration Risk [Line Items]  
Number of full-time employees 2,650dei_EntityNumberOfEmployees
Employees Subject To Collective Bargaining Agreements [Member] | Labor Force Concentration Risk [Member] | Number of Employees [Member]  
Concentration Risk [Line Items]  
Concentration risk, percentage 49.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_CollectiveBargainingArrangementAxis
= cehe_EmployeesSubjectToCollectiveBargainingAgreementsMember
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_NumberOfEmployeesTotalMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_LaborForceConcentrationRiskMember