Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Con Edison [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 59	$ 48	$ 177	$ 142
Interest cost on projected benefit obligation	137	140	410	420
Expected return on plan assets	(176)	(184)	(528)	(550)
Amortization of net actuarial loss	177	133	531	397
Amortization of prior service costs	2	2	6	6
NET PERIODIC BENEFIT COST	199	139	596	415
Amortization of regulatory asset			1	1
TOTAL PERIODIC BENEFIT COST			597	416
Cost capitalized	(64)	(45)	(200)	(141)
Reconciliation to rate level		(11)	(37)	(68)
Cost charged to operating expenses	135	83	360	207
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	55	45	165	133
Interest cost on projected benefit obligation	128	131	385	393
Expected return on plan assets	(168)	(174)	(503)	(524)
Amortization of net actuarial loss	168	126	503	376
Amortization of prior service costs	2		4	4
NET PERIODIC BENEFIT COST	185	128	554	382
Amortization of regulatory asset			1	1
TOTAL PERIODIC BENEFIT COST			555	383
Cost capitalized	(60)	(42)	(186)	(131)
Reconciliation to rate level	(1)	(11)	(36)	(70)
Cost charged to operating expenses	$ 124	$ 75	$ 333	$ 182