Pension Benefits - Total Periodic Benefit Costs (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	$ 72	$ 66
Interest cost on projected benefit obligation	140	148
Expected return on plan assets	(258)	(243)
Recognition of net actuarial loss	172	149
Recognition of prior service costs	(4)	(4)
TOTAL PERIODIC BENEFIT COST	122	116
Cost capitalized	(31)	(43)
Reconciliation to rate level	(23)	(11)
Cost charged to operating expenses	68	62
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost – including administrative expenses	68	61
Interest cost on projected benefit obligation	131	139
Expected return on plan assets	(245)	(229)
Recognition of net actuarial loss	163	141
Recognition of prior service costs	(5)	(5)
TOTAL PERIODIC BENEFIT COST	112	107
Cost capitalized	(29)	(41)
Reconciliation to rate level	(25)	(12)
Cost charged to operating expenses	$ 58	$ 54