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Short-Term Borrowing - Additional Information (Detail)
12 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Oct. 31, 2011
Short-term Debt [Line Items]      
Credit facility expiration date Oct. 31, 2017    
Commercial paper, outstanding $ 1,529,000,000 $ 800,000,000  
Weighted average interest rate 0.70% 0.40%  
Loans outstanding under credit agreement $ 0 $ 0  
Letters of credit outstanding under the Credit Agreement $ 15,000,000 11,000,000  
Ratio of consolidated debt to consolidated total capital 0.52    
Minimum percentage of liens on assets 5.00%    
October 2016      
Short-term Debt [Line Items]      
Current amount available $ 1,500,000,000    
Maximum      
Short-term Debt [Line Items]      
Ratio of consolidated debt to consolidated total capital     0.65
Letters of Credit | October 2016      
Short-term Debt [Line Items]      
Maximum credit available 2,250,000,000    
Maximum borrowing capacity 1,200,000,000    
Letters of Credit | October 2017      
Short-term Debt [Line Items]      
Maximum credit available 2,100,000,000    
CECONY      
Short-term Debt [Line Items]      
Commercial paper, outstanding 1,033,000,000 450,000,000  
Letters of credit outstanding under the Credit Agreement $ 11,000,000 $ 11,000,000