Other Postretirement Benefits - Total Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4	$ 10	$ 9
Interest cost on accumulated other postretirement benefit obligation	11	12	23	24
Expected return on plan assets	(17)	(19)	(35)	(38)
Recognition of net actuarial loss/(gain)	1	1	1	2
Recognition of prior service cost	(4)	(5)	(8)	(10)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	(4)	(7)	(9)	(13)
Cost capitalized	2	2	4	3
Reconciliation to rate level	(1)	7	(2)	14
Cost charged to operating expenses	(3)	2	(7)	4
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	7	7
Interest cost on accumulated other postretirement benefit obligation	10	10	19	20
Expected return on plan assets	(15)	(17)	(30)	(34)
Recognition of net actuarial loss/(gain)	(1)	1	(2)	1
Recognition of prior service cost	(3)	(3)	(6)	(7)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	(6)	(6)	(12)	(13)
Cost capitalized	3	2	5	3
Reconciliation to rate level	(1)	6	(1)	14
Cost charged to operating expenses	$ (4)	$ 2	$ (8)	$ 4