Stock-Based Compensation - Summary of Status of Stock Options Awarded (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 43.046
Weighted Average Exercise Price, Exercised	$ 43.128
Weighted Average Exercise Price, Forfeited	$ 41.665
Weighted Average Exercise Price Outstanding, Ending Balance	$ 43.008
Outstanding Shares, Beginning Balance	927,025
Exercised, Shares	(318,550)
Forfeited, Shares	(2,000)
Outstanding Shares, Ending Balance	606,475
CECONY [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 43.066
Weighted Average Exercise Price, Exercised	$ 43.238
Weighted Average Exercise Price, Forfeited	$ 43.005
Weighted Average Exercise Price Outstanding, Ending Balance	$ 42.973
Outstanding Shares, Beginning Balance	740,875
Exercised, Shares	(258,700)
Forfeited, Shares	(1,000)
Outstanding Shares, Ending Balance	481,175