Other Postretirement Benefits - Net Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18	$ 20	$ 19
Interest cost on accumulated other postretirement benefit obligation	48	51	60
Expected return on plan assets	(77)	(78)	(77)
Recognition of net actuarial loss	5	31	57
Recognition of prior service cost	(20)	(20)	(19)
NET PERIODIC BENEFIT COST	(26)	4	40
Cost capitalized	11	(2)	(15)
Reconciliation to rate level	22	14	10
Cost charged to operating expenses	7	16	35
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	13	15	15
Interest cost on accumulated other postretirement benefit obligation	40	43	52
Expected return on plan assets	(67)	(68)	(68)
Recognition of net actuarial loss	3	28	51
Recognition of prior service cost	(14)	(14)	(15)
NET PERIODIC BENEFIT COST	(25)	4	35
Cost capitalized	10	(2)	(14)
Reconciliation to rate level	22	6	2
Cost charged to operating expenses	$ 7	$ 8	$ 23