Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 57	$ 67
Interest cost on projected benefit obligation	143	134
Expected return on plan assets	(208)	(187)
Recognition of net actuarial loss	154	208
Recognition of prior service costs	1	1
NET PERIODIC BENEFIT COST	147	223
Cost capitalized	(51)	(82)
Reconciliation to rate level	26	11
Cost charged to operating expenses	122	152
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	53	62
Interest cost on projected benefit obligation	134	126
Expected return on plan assets	(197)	(178)
Recognition of net actuarial loss	146	197
Recognition of prior service costs	1	1
NET PERIODIC BENEFIT COST	137	208
Cost capitalized	(49)	(79)
Reconciliation to rate level	23	13
Cost charged to operating expenses	$ 111	$ 142