Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 23	$ 26	$ 26
Interest cost on accumulated other postretirement benefit obligation	54	73	83
Expected return on plan assets	(77)	(85)	(88)
Recognition of net actuarial loss	65	98	88
Recognition of prior service cost	(27)	(21)	(10)
Recognition of transition obligation		2	4
NET PERIODIC BENEFIT COST	38	93	103
Cost capitalized	(15)	(32)	(35)
Reconciliation to rate level	58	20	14
Cost charged to operating expenses	81	81	82
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	18	21	20
Interest cost on accumulated other postretirement benefit obligation	46	63	72
Expected return on plan assets	(68)	(75)	(78)
Recognition of net actuarial loss	57	87	80
Recognition of prior service cost	(23)	(18)	(11)
Recognition of transition obligation		2	4
NET PERIODIC BENEFIT COST	30	80	87
Cost capitalized	(12)	(28)	(29)
Reconciliation to rate level	50	16	13
Cost charged to operating expenses	$ 68	$ 68	$ 71