Short-Term Borrowing - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Credit facility expiry date	Oct. 31, 2016
Maximum borrowing capacity	$ 2,250,000,000
Current amount available	1,000,000,000
Commercial paper, outstanding	539,000,000
Weighted average interest rate	0.30%
Line of credit facility, covenant terms	Ratio of consolidated debt to consolidated total capital of 0.65 to 1 (at December 31, 2012 this ratio was 0.49 to 1 for Con Edison and CECONY); having liens on its assets in an aggregate amount exceeding 5 percent of its consolidated total capital, subject to certain exceptions; and the failure, following any applicable notice period, to meet certain other customary covenants.
Letters of credit outstanding under the credit agreement	131,000,000	173,000,000
CECONY [Member]
Short-term Debt [Line Items]
Commercial paper, outstanding	421,000,000
Weighted average interest rate	0.30%
Letters of credit outstanding under the credit agreement	121,000,000	150,000,000
Letter Of Credit [Member]
Short-term Debt [Line Items]
Current amount available	$ 1,200,000,000