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Variable Interest Entities - Schedule of Sale and Deconsolidation of a Variable Interest Entity (Parenthetical) (Detail) (California Solar [Member], USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
California Solar [Member]
  
Variable Interest Entity [Line Items]  
Transaction costs $ 1ed_TransactionCosts
/ dei_LegalEntityAxis
= ed_CEDCaliforniaHoldingsMember