Other Postretirement Benefits - Total Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4
Interest cost on accumulated other postretirement benefit obligation	11	12
Expected return on plan assets	(17)	(19)
Recognition of net actuarial loss	1	1
Recognition of prior service cost	(4)	(5)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	(4)	(7)
Cost capitalized	2	2
Reconciliation to rate level	(1)	7
Cost charged to operating expenses	(3)	2
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3
Interest cost on accumulated other postretirement benefit obligation	10	10
Expected return on plan assets	(15)	(17)
Recognition of net actuarial loss	(1)	1
Recognition of prior service cost	(3)	(4)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	(6)	(7)
Cost capitalized	2	2
Reconciliation to rate level	0	7
Cost charged to operating expenses	$ (4)	$ 2