Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 5	$ 15	$ 15
Interest cost on accumulated other postretirement benefit obligation	11	11	32	34
Expected return on plan assets	(18)	(17)	(55)	(52)
Recognition of net actuarial loss/(gain)	2	1	6	2
Recognition of prior service cost/(credit)	(2)	(5)	(5)	(13)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	(2)	(5)	(7)	(14)
Cost capitalized	(2)	2	(6)	6
Reconciliation to rate level	2	(1)	6	(3)
Total expense/(credit) recognized	(2)	(4)	(7)	(11)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	10	10
Interest cost on accumulated other postretirement benefit obligation	9	9	26	28
Expected return on plan assets	(16)	(15)	(47)	(45)
Recognition of net actuarial loss/(gain)	1	0	2	(2)
Recognition of prior service cost/(credit)	(1)	(3)	(2)	(9)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	(4)	(6)	(11)	(18)
Cost capitalized	(1)	2	(4)	7
Reconciliation to rate level	2	0	7	(1)
Total expense/(credit) recognized	$ (3)	$ (4)	$ (8)	$ (12)