Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CECONY [Member]
Sale of natural gas	$ 54	$ 81	$ 99
Funding limit of CECONY to O&R	250
O & R [Member]
Outstanding loans to O&R	$ 0	$ 0