Related Party Transactions - Additional Information (Details)	7 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) MMBTU agreement	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 30, 2016	Jan. 31, 2016
Related Party Transaction [Line Items]
Gas purchased for resale		$ 808,000,000	$ 477,000,000	$ 495,000,000
CECONY
Related Party Transaction [Line Items]
Sale of natural gas		66,000,000	47,000,000	54,000,000
Gas purchased for resale		510,000,000	319,000,000	$ 337,000,000
Funding limit of CECONY to O&R (not to exceed)		$ 250,000,000
CECONY | Related Party, Lending of Funds
Related Party Transaction [Line Items]
Lending period (not more than) (months)		12 months
CECONY | Equity Method Investee | Mountain Valley Pipeline
Related Party Transaction [Line Items]
Transportation contract term		20 years
Generating capacity per day (in dekatherms) | MMBTU		250,000
Amount of transaction		$ 0
CECONY | Equity Method Investee | Stagecoach | Purchased Power Costs
Related Party Transaction [Line Items]
Gas purchased for resale	$ 49,000,000
CECONY | Equity Method Investee | Stagecoach | Purchased Power Costs | Clean Energy Businesses
Related Party Transaction [Line Items]
Number of electricity sales agreements entered into | agreement		2
CECONY | Affiliated Entity | Financial Electric Capacity Contract | Con Edison Energy
Related Party Transaction [Line Items]
Amount of transaction		$ 3,000,000	0
CET Electric
Related Party Transaction [Line Items]
Ownership interest, percentage		45.70%
CET Gas | Stagecoach
Related Party Transaction [Line Items]
Percentage of equity interest owned					50.00%
CET Gas | Mountain Valley Pipeline
Related Party Transaction [Line Items]
Percentage of equity interest owned		12.50%				12.50%
O&R
Related Party Transaction [Line Items]
Outstanding loans to O&R		$ 0	$ 0