Pension Benefits - Total Periodic Benefit Costs (Detail) - Pension Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 69	$ 74
Interest cost on projected benefit obligation	149	144
Expected return on plan assets	(237)	(222)
Recognition of net actuarial loss	149	194
Recognition of prior service costs	1	1
TOTAL PERIODIC BENEFIT COST	131	191
Cost capitalized	(52)	(68)
Reconciliation to rate level	12	(24)
Cost charged to operating expenses	91	99
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	65	70
Interest cost on projected benefit obligation	140	135
Expected return on plan assets	(225)	(210)
Recognition of net actuarial loss	141	183
Recognition of prior service costs	0	0
TOTAL PERIODIC BENEFIT COST	121	178
Cost capitalized	(49)	(65)
Reconciliation to rate level	13	(24)
Cost charged to operating expenses	$ 85	$ 89