Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Con Edison [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	$ 6	$ 7	$ 20	$ 19
Interest cost on accumulated other postretirement benefit obligation	18	20	55	62
Expected return on plan assets	(21)	(22)	(64)	(66)
Amortization of net actuarial loss	24	22	73	66
Amortization of prior service cost	(5)	(3)	(16)	(7)
Amortization of transition obligation		1	1	3
NET PERIODIC BENEFIT COST	22	25	69	77
Cost capitalized	(8)	(9)	(24)	(27)
Reconciliation to rate level	3	3	15	12
Cost charged to operating expenses	17	19	60	62
CECONY [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Service cost	5	5	15	15
Interest cost on accumulated other postretirement benefit obligation	16	18	48	54
Expected return on plan assets	(19)	(21)	(56)	(59)
Amortization of net actuarial loss	22	20	65	60
Amortization of prior service cost	(4)	(3)	(13)	(9)
Amortization of transition obligation		1	1	3
NET PERIODIC BENEFIT COST	20	20	60	64
Cost capitalized	(7)	(7)	(20)	(22)
Reconciliation to rate level	3	3	12	10
Cost charged to operating expenses	$ 16	$ 16	$ 52	$ 52