Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 67	$ 59	$ 133	$ 118
Interest cost on projected benefit obligation	134	137	268	274
Expected return on plan assets	(187)	(177)	(375)	(352)
Recognition of net actuarial loss	208	177	416	354
Recognition of prior service costs	1	2	3	4
NET PERIODIC BENEFIT COST	223	198	445	398
Amortization of regulatory asset	1	1	1	1
TOTAL PERIODIC BENEFIT COST	224	199	446	399
Cost capitalized	(88)	(68)	(170)	(135)
Reconciliation to rate level	(30)	3	(24)	(32)
Cost charged to operating expenses	106	134	252	232
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	62	55	124	110
Interest cost on projected benefit obligation	126	128	252	257
Expected return on plan assets	(178)	(168)	(356)	(335)
Recognition of net actuarial loss	197	168	394	335
Recognition of prior service costs	1	2	2	3
NET PERIODIC BENEFIT COST	208	185	416	370
Amortization of regulatory asset	1	1	1	1
TOTAL PERIODIC BENEFIT COST	209	186	417	371
Cost capitalized	(84)	(63)	(163)	(126)
Reconciliation to rate level	(29)	2	(23)	(36)
Cost charged to operating expenses	$ 96	$ 125	$ 231	$ 209