Pension Benefits - Total Periodic Benefit Costs (Detail) - Pension Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 69	$ 74	$ 138	$ 149
Interest cost on projected benefit obligation	149	144	298	287
Expected return on plan assets	(237)	(222)	(474)	(443)
Recognition of net actuarial loss	149	194	298	388
Recognition of prior service costs	1	1	2	2
NET PERIODIC BENEFIT COST	131	191	262	383
Amortization of regulatory asset	0	1	0	1
TOTAL PERIODIC BENEFIT COST	131	192	262	384
Cost capitalized	(53)	(76)	(106)	(144)
Reconciliation to rate level	13	(17)	26	(42)
Cost charged to operating expenses	91	99	182	198
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	65	70	129	139
Interest cost on projected benefit obligation	140	135	280	269
Expected return on plan assets	(225)	(210)	(449)	(420)
Recognition of net actuarial loss	141	183	282	367
Recognition of prior service costs	0	0	1	1
NET PERIODIC BENEFIT COST	121	178	243	356
Amortization of regulatory asset	0	1	0	1
TOTAL PERIODIC BENEFIT COST	121	179	243	357
Cost capitalized	(50)	(72)	(99)	(137)
Reconciliation to rate level	14	(18)	26	(42)
Cost charged to operating expenses	$ 85	$ 89	$ 170	$ 178