Pension Benefits - Companies' Net Periodic Benefit Costs (Detail) (Pension 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 - including administrative expenses	$ 267	$ 237	$ 190
Interest cost on projected benefit obligation	537	547	560
Expected return on plan assets	(750)	(705)	(734)
Recognition of net actuarial loss	832	709	530
Recognition of prior service costs	5	8	8
NET PERIODIC BENEFIT COST	891	796	554
Amortization of regulatory asset	2	2	2
TOTAL PERIODIC BENEFIT COST	893	798	556
Cost capitalized	(348)	(277)	(185)
Reconciliation to rate level	(84)	(8)	(65)
Cost charged to operating expenses	461	513	306
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	249	220	177
Interest cost on projected benefit obligation	503	513	524
Expected return on plan assets	(713)	(670)	(698)
Recognition of net actuarial loss	788	670	501
Recognition of prior service costs	4	6	6
NET PERIODIC BENEFIT COST	831	739	510
Amortization of regulatory asset	2	2	2
TOTAL PERIODIC BENEFIT COST	833	741	512
Cost capitalized	(327)	(260)	(172)
Reconciliation to rate level	(87)	(12)	(68)
Cost charged to operating expenses	$ 419	$ 469	$ 272