Leases - Additional Information (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Assets under finance leases	$ 2	$ 2
Finance leases, accumulated amortization	5	5
Right-of-use asset obtained in exchange for operating lease liability	2	3
CECONY
Lessee, Lease, Description [Line Items]
Assets under finance leases	1	1
Finance leases, accumulated amortization	3	3
Right-of-use asset obtained in exchange for operating lease liability	$ 1	$ 2
Minimum
Lessee, Lease, Description [Line Items]
Lease, term	1 year	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease, term	35 years	35 years
Lease, renewal term	5 years	5 years