Related Party Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CECONY [Member]
Sale of natural gas	$ 123	$ 54	$ 81
Funding limit of CECONY to O&R	250
O&R [Member]
Outstanding loans to O&R	$ 0	$ 0