Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension Plan [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 57	$ 67	$ 170	$ 200
Interest cost on projected benefit obligation	143	134	429	403
Expected return on plan assets	(208)	(187)	(624)	(563)
Recognition of net actuarial loss	154	208	464	624
Recognition of prior service costs	1	1	3	4
NET PERIODIC BENEFIT COST	147	223	442	668
Amortization of regulatory asset	1	1	2	2
TOTAL PERIODIC BENEFIT COST	148	224	444	670
Cost capitalized	(57)	(86)	(166)	(256)
Reconciliation to rate level	30	(31)	86	(55)
Cost charged to operating expenses	121	107	364	359
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	53	62	158	186
Interest cost on projected benefit obligation	134	126	402	377
Expected return on plan assets	(198)	(178)	(592)	(534)
Recognition of net actuarial loss	146	197	439	591
Recognition of prior service costs	1	1	2	3
NET PERIODIC BENEFIT COST	136	208	409	623
Amortization of regulatory asset	1	1	2	2
TOTAL PERIODIC BENEFIT COST	137	209	411	625
Cost capitalized	(54)	(78)	(156)	(241)
Reconciliation to rate level	28	(34)	78	(56)
Cost charged to operating expenses	$ 111	$ 97	$ 333	$ 328