Other Postretirement Benefits - Additional Information (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	$ 6
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	$ 6

Amount of employer's best estimate of contributions expected to be paid to the plan in the current remaining fiscal period.

No definition available.

Name:	us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration