Leases - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Lease, renewal term	5 years
Assets under finance leases	$ 3	$ 1
Finance leases, accumulated amortization	3	5
Right-of-use asset obtained in exchange for operating lease liability	23	39
CECONY
Lessee, Lease, Description [Line Items]
Assets under finance leases	2
Finance leases, accumulated amortization	1	3
Right-of-use asset obtained in exchange for operating lease liability	$ 11	$ 4
Minimum
Lessee, Lease, Description [Line Items]
Lease, term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease, term	40 years