Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Assets under finance leases	$ 2		$ 2		$ 3
Finance leases, accumulated amortization	3		3		3
Right-of-use assets	15	$ 8	32	$ 13
CECONY | Subsidiaries
Lessee, Lease, Description [Line Items]
Assets under finance leases	1		1		2
Finance leases, accumulated amortization	2		2		$ 1
Right-of-use assets	$ 5	$ 2	$ 7	$ 3