Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Assets under finance leases	$ 3		$ 3		$ 3
Finance leases, accumulated amortization	3		3		3
Right-of-use assets	1	$ 5	18	$ 5
CECONY | Subsidiaries
Lessee, Lease, Description [Line Items]
Assets under finance leases	2		2		2
Finance leases, accumulated amortization	1		1		$ 1
Right-of-use assets	$ 0	$ 1	$ 1	$ 1