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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 67	$ 59	$ 200	$ 177
Interest cost on projected benefit obligation	134	137	403	410
Expected return on plan assets	(187)	(176)	(563)	(528)
Recognition of net actuarial loss	208	177	624	531
Recognition of prior service costs	1	2	4	6
NET PERIODIC BENEFIT COST	223	199	668	596
Amortization of regulatory asset	1		2	1
TOTAL PERIODIC BENEFIT COST	224	199	670	597
Cost capitalized	(86)	(64)	(256)	(200)
Reconciliation to rate level	(31)		(55)	(37)
Cost charged to operating expenses	107	135	359	360
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	62	55	186	165
Interest cost on projected benefit obligation	126	128	377	385
Expected return on plan assets	(178)	(168)	(534)	(503)
Recognition of net actuarial loss	197	168	591	503
Recognition of prior service costs	1	2	3	4
NET PERIODIC BENEFIT COST	208	185	623	554
Amortization of regulatory asset	1		2	1
TOTAL PERIODIC BENEFIT COST	209	185	625	555
Cost capitalized	(78)	(60)	(241)	(186)
Reconciliation to rate level	(34)	(1)	(56)	(36)
Cost charged to operating expenses	$ 97	$ 124	$ 328	$ 333