Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	$ 6	$ 6	$ 18	$ 20
Interest cost on accumulated other postretirement benefit obligation	13	18	40	55
Expected return on plan assets	(19)	(21)	(58)	(64)
Recognition of net actuarial loss	16	24	48	73
Recognition of prior service cost	(7)	(5)	(20)	(16)
Recognition of transition obligation				1
NET PERIODIC BENEFIT COST	9	22	28	69
Cost capitalized	(3)	(8)	(10)	(24)
Reconciliation to rate level	14	3	43	15
Cost charged to operating expenses	20	17	61	60
CECONY [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	5	5	14	15
Interest cost on accumulated other postretirement benefit obligation	12	16	34	48
Expected return on plan assets	(17)	(19)	(51)	(56)
Recognition of net actuarial loss	14	22	43	65
Recognition of prior service cost	(6)	(4)	(17)	(13)
Recognition of transition obligation				1
NET PERIODIC BENEFIT COST	8	20	23	60
Cost capitalized	(3)	(7)	(9)	(20)
Reconciliation to rate level	12	3	37	12
Cost charged to operating expenses	$ 17	$ 16	$ 51	$ 52