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Environmental Matters - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Site Contingency [Line Items]          
Insurance recoveries $ 0 $ 1 $ 0 $ 1  
CECONY          
Site Contingency [Line Items]          
Insurance recoveries $ 0 $ 1 $ 0 $ 1  
CECONY | Asbestos Proceedings          
Site Contingency [Line Items]          
Estimated undiscounted asbestos liability (years)     15 years    
Superfund Sites | Manufactured Gas Plant Sites | Maximum          
Site Contingency [Line Items]          
Estimated aggregate undiscounted potential liability related environmental contaminants (up to)         $ 2,800
Superfund Sites | Manufactured Gas Plant Sites | Maximum | CECONY          
Site Contingency [Line Items]          
Estimated aggregate undiscounted potential liability related environmental contaminants (up to)         $ 2,600