Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Detail) (Other Postretirement Benefits [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 6	$ 10	$ 12
Interest cost on accumulated other postretirement benefit obligation	15	13	30	27
Expected return on plan assets	(19)	(19)	(38)	(39)
Recognition of net actuarial loss	14	16	28	32
Recognition of prior service cost	(5)	(7)	(10)	(13)
NET PERIODIC POSTRETIREMENT BENEFIT COST	10	9	20	19
Cost capitalized	(4)	(4)	(8)	(7)
Reconciliation to rate level	3	16	6	29
Cost charged to operating expenses	9	21	18	41
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5	7	9
Interest cost on accumulated other postretirement benefit obligation	13	12	26	23
Expected return on plan assets	(17)	(17)	(34)	(34)
Recognition of net actuarial loss	13	14	26	28
Recognition of prior service cost	(4)	(6)	(7)	(11)
NET PERIODIC POSTRETIREMENT BENEFIT COST	9	8	18	15
Cost capitalized	(4)	(4)	(7)	(6)
Reconciliation to rate level	1	13	1	25
Cost charged to operating expenses	$ 6	$ 17	$ 12	$ 34