Other Postretirement Benefits - Periodic Postretirement Benefit Costs (Details) - Other Postretirement Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 7	$ 5
Interest cost on projected other postretirement benefit obligation	8	9
Expected return on plan assets	(17)	(16)
Recognition of net actuarial loss/(gain)	6	27
Recognition of prior service credit	(1)	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	3	24
Cost capitalized	(3)	(2)
Reconciliation to rate level	0	(22)
Total expense/(credit) recognized	0	0
CECONY
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	5	4
Interest cost on projected other postretirement benefit obligation	7	8
Expected return on plan assets	(14)	(14)
Recognition of net actuarial loss/(gain)	5	27
Recognition of prior service credit	0	(1)
TOTAL PERIODIC OTHER POSTRETIREMENT BENEFIT COST	3	24
Cost capitalized	(2)	(1)
Reconciliation to rate level	(2)	(24)
Total expense/(credit) recognized	$ (1)	$ (1)