Capitalization - Additional Information (Detail) (USD $) In Millions, unless otherwise specified							1 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Level 2 [Member]	Mar. 31, 2014 Level 3 [Member]	Mar. 31, 2014 CECONY [Member]	Dec. 31, 2013 CECONY [Member]	Feb. 28, 2014 CECONY [Member] 4.70 Percent Debentures [Member]	Mar. 31, 2014 CECONY [Member] 4.45 Percent Debentures [Member]	Mar. 31, 2014 CECONY [Member] Level 2 [Member]	Mar. 31, 2014 CECONY [Member] Level 3 [Member]
Schedule of Capitalization [Line Items]
Debentures redeemed at maturity							$ 200
Debentures interest rate							4.70%	4.45%
Period of debentures							10 years	30 years
Debentures issued								850
Long-term debt, fair value	13,000	12,082	12,364	636	11,692	10,797			11,056	636
Tax - exempt debt										$ 636