Other Postretirement Benefits - Schedule of Change of Assumed Health Care Cost Trend Rate (Detail) (Scenario, Forecast [Member], Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Effect on accumulated other postretirement benefit obligation, Increase	$ (35)
Effect on service cost and interest cost components for 2013, Increase	(2)
Effect on accumulated other postretirement benefit obligation, Decrease	27
Effect on service cost and interest cost components for 2013, Decrease	1
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Effect on accumulated other postretirement benefit obligation, Increase	(53)
Effect on service cost and interest cost components for 2013, Increase	(4)
Effect on accumulated other postretirement benefit obligation, Decrease	41
Effect on service cost and interest cost components for 2013, Decrease	$ 3