Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension Plan [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 57	$ 67	$ 113	$ 133
Interest cost on projected benefit obligation	143	134	286	268
Expected return on plan assets	(208)	(187)	(416)	(375)
Recognition of net actuarial loss	154	208	309	416
Recognition of prior service costs	1	1	2	3
NET PERIODIC BENEFIT COST	147	223	294	445
Amortization of regulatory asset	1	1	1	1
TOTAL PERIODIC BENEFIT COST	148	224	295	446
Cost capitalized	(57)	(88)	(109)	(170)
Reconciliation to rate level	30	(30)	57	(24)
Cost charged to operating expenses	121	106	243	252
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	53	62	106	124
Interest cost on projected benefit obligation	134	126	268	252
Expected return on plan assets	(198)	(178)	(395)	(356)
Recognition of net actuarial loss	146	197	293	394
Recognition of prior service costs	1	1	1	2
NET PERIODIC BENEFIT COST	136	208	273	416
Amortization of regulatory asset	1	1	1	1
TOTAL PERIODIC BENEFIT COST	137	209	274	417
Cost capitalized	(54)	(84)	(103)	(163)
Reconciliation to rate level	28	(29)	51	(23)
Cost charged to operating expenses	$ 111	$ 96	$ 222	$ 231