Pension Benefits - Total Periodic Benefit Costs (Detail) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 297	$ 227	$ 267
Interest cost on projected benefit obligation	575	572	537
Expected return on plan assets	(886)	(832)	(750)
Recognition of net actuarial loss	775	618	832
Recognition of prior service costs	4	4	5
NET PERIODIC BENEFIT COST	765	589	891
Amortization of regulatory asset	1	2	2
TOTAL PERIODIC BENEFIT COST	766	591	893
Cost capitalized	(301)	(225)	(348)
Reconciliation to rate level	(74)	118	(84)
Cost charged to operating expenses	391	484	461
Increase in CECONY's pension obligation	45
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	279	211	249
Interest cost on projected benefit obligation	538	536	503
Expected return on plan assets	(840)	(789)	(713)
Recognition of net actuarial loss	734	586	788
Recognition of prior service costs	2	2	4
NET PERIODIC BENEFIT COST	713	546	831
Amortization of regulatory asset	1	2	2
TOTAL PERIODIC BENEFIT COST	714	548	833
Cost capitalized	(285)	(212)	(327)
Reconciliation to rate level	(74)	108	(87)
Cost charged to operating expenses	$ 355	$ 444	$ 419