Other Postretirement Benefits - Schedule of Change of Assumed Health Care Cost Trend Rate (Detail) - Scenario, Forecast - Other Postretirement Benefits $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Effect on accumulated other postretirement benefit obligation, Increase	$ (18)
Effect on service cost and interest cost components for 2015, Increase	(1)
Effect on accumulated other postretirement benefit obligation, Decrease	41
Effect on service cost and interest cost components for 2015, Decrease	1
CECONY
Defined Benefit Plan Disclosure [Line Items]
Effect on accumulated other postretirement benefit obligation, Increase	(37)
Effect on service cost and interest cost components for 2015, Increase	(3)
Effect on accumulated other postretirement benefit obligation, Decrease	56
Effect on service cost and interest cost components for 2015, Decrease	$ 2