Capitalization - Additional Information (Detail) (USD $) In Millions, unless otherwise specified							1 Months Ended				9 Months Ended	1 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Level 2 [Member]	Sep. 30, 2014 Level 3 [Member]	Sep. 30, 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]	Apr. 30, 2014 CECONY [Member] 5.55 Percent Debentures [Member]	Sep. 30, 2014 CECONY [Member] Level 2 [Member]	Sep. 30, 2014 CECONY [Member] Level 3 [Member]	May 31, 2014 CCH [Member]
Schedule of Capitalization [Line Items]
Debentures redeemed at maturity							$ 200		$ 275
Debentures interest rate							4.70%	4.45%	5.55%
Period of debentures							10 years	30 years	5 years
Debentures issued								850
Deconsolidated long term debt	11,195	10,974			10,216	9,841						217
Percentage of variable interests sold												50.00%
Long-term debt, fair value	12,696	12,082	12,060	636	11,537	10,797				10,901	636
Tax-exempt debt											$ 636