Pension Benefits - Total Periodic Benefit Costs (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 66	$ 69	$ 197	$ 207
Interest cost on projected benefit obligation	148	149	444	447
Expected return on plan assets	(243)	(237)	(726)	(711)
Recognition of net actuarial loss	149	149	446	447
Recognition of prior service costs	(4)	1	(13)	3
TOTAL PERIODIC BENEFIT COST	116	131	348	393
Cost capitalized	(40)	(51)	(134)	(157)
Reconciliation to rate level	(14)	10	(28)	35
Cost charged to operating expenses	62	90	186	271
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	61	65	184	194
Interest cost on projected benefit obligation	139	140	416	419
Expected return on plan assets	(229)	(225)	(689)	(674)
Recognition of net actuarial loss	141	141	423	424
Recognition of prior service costs	(5)	0	(14)	1
TOTAL PERIODIC BENEFIT COST	107	121	320	364
Cost capitalized	(37)	(49)	(125)	(148)
Reconciliation to rate level	(16)	13	(32)	39
Cost charged to operating expenses	$ 54	$ 85	$ 163	$ 255