Capitalization - Additional Information (Detail) (USD $)					1 Months Ended			1 Months Ended
	Sep. 30, 2012 Consolidated Edison Inc [Member]	Dec. 31, 2011 Consolidated Edison Inc [Member]	Sep. 30, 2012 Consolidated Edison Inc [Member] Level 2 [Member]	Sep. 30, 2012 Consolidated Edison Inc [Member] Level 3 [Member]	Mar. 31, 2012 CECONY [Member]	Sep. 30, 2012 CECONY [Member]	Dec. 31, 2011 CECONY [Member]	Nov. 30, 2012 CECONY [Member] Subsequent Event [Member]	Sep. 30, 2012 CECONY [Member] Level 2 [Member]	Sep. 30, 2012 CECONY [Member] Level 3 [Member]
Issue of debentures					$ 400,000,000
Rate of debentures					4.20%
Period of debentures					30 years
Net proceeds from the sale					239,000,000
Redemption of Cumulative Preferred Stock					5
Cumulative Preferred Stock, par value					$ 100
Tax-exempt debt								225,000,000
Fair values of long-term debt	$ 13,197,000,000	$ 12,744,000,000	$ 12,561,000,000	$ 636,000,000		$ 12,001,000,000	$ 11,593,000,000		$ 11,365,000,000	$ 636,000,000