Other Postretirement Benefits - Total Periodic Postretirement Benefit Costs (Details) - Other Postretirement 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	$ 5	$ 4	$ 15	$ 13
Interest cost on accumulated other postretirement benefit obligation	11	12	34	36
Expected return on plan assets	(17)	(19)	(52)	(58)
Recognition of net actuarial loss/(gain)	1	1	2	4
Recognition of prior service cost	(5)	(5)	(13)	(15)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	(5)	(7)	(14)	(20)
Cost capitalized	2	2	6	5
Reconciliation to rate level	(1)	7	(3)	20
Cost charged to operating expenses	(4)	2	(11)	5
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	10	10
Interest cost on accumulated other postretirement benefit obligation	9	10	28	30
Expected return on plan assets	(15)	(17)	(45)	(50)
Recognition of net actuarial loss/(gain)	0	1	(2)	2
Recognition of prior service cost	(3)	(3)	(9)	(11)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	(6)	(6)	(18)	(19)
Cost capitalized	2	2	7	5
Reconciliation to rate level	0	6	(1)	19
Cost charged to operating expenses	$ (4)	$ 2	$ (12)	$ 5