Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4
Interest cost on accumulated other postretirement benefit obligation	9	11
Expected return on plan assets	(16)	(16)
Recognition of net actuarial loss/(gain)	27	(2)
Recognition of prior service credit	(1)	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	24	(4)
Cost capitalized	(2)	(2)
Reconciliation to rate level	(22)	3
Total credit recognized	0	(3)
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3
Interest cost on accumulated other postretirement benefit obligation	8	9
Expected return on plan assets	(14)	(14)
Recognition of net actuarial loss/(gain)	27	(2)
Recognition of prior service credit	(1)	0
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST/(CREDIT)	24	(4)
Cost capitalized	(1)	(2)
Reconciliation to rate level	(24)	2
Total credit recognized	$ (1)	$ (4)