Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Assets under finance leases	$ 3	$ 3		$ 1
Finance leases, accumulated amortization	3	3		5
Right-of-use assets	8	13
CECONY
Lessee, Lease, Description [Line Items]
Assets under finance leases	2	2
Finance leases, accumulated amortization	1	$ 1		$ 3
Right-of-use assets	$ 2		$ 3