Capitalization - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended					1 Months Ended					9 Months Ended
	Apr. 30, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Level 2 [Member]	Sep. 30, 2013 Level 3 [Member]	Jun. 30, 2013 CECONY [Member]	Feb. 28, 2013 CECONY [Member]	Sep. 30, 2013 CECONY [Member]	Dec. 31, 2012 CECONY [Member]	Sep. 30, 2013 CECONY [Member] Level 2 [Member]	Sep. 30, 2013 CECONY [Member] Level 3 [Member]
Schedule of Capitalization [Line Items]
Debentures issued							$ 700
Debentures interest rate	4.78%						3.95%
Period of debentures							30 years
Redeemable debentures						200	500
Redeemable debentures interest rate						3.85%	4.875%
Period of redeemable debentures						10 years	10 years
Senior notes issued	219
Senior notes weighted average life	15 years
Senior notes maturity date	2037
Long-term debt, fair value		12,213	12,935	11,577	636			10,925	11,751	10,289	636
Tax - exempt debt											$ 636