Capitalization - Additional Information (Detail) (USD $) In Millions, unless otherwise specified			1 Months Ended							3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Apr. 30, 2013 Subsequent Event [Member]	Feb. 28, 2013 CECONY [Member]	Mar. 31, 2013 CECONY [Member]	Dec. 31, 2012 CECONY [Member]	Mar. 31, 2013 Level 2 [Member]	Mar. 31, 2013 Level 2 [Member] CECONY [Member]	Mar. 31, 2013 Level 3 [Member]	Mar. 31, 2013 Level 3 [Member] CECONY [Member]
Schedule of Capitalization [Line Items]
Debentures issued				$ 700
Debentures interest rate			4.78%	3.95%
Period of debentures				30 years
Redeemable debentures				500
Redeemable debentures interest rate				4.875%
Period of redeemable debentures				10 years
Senior notes issued			219
Senior notes weighted average life			15 years
Senior notes maturity date			2037
Long-term debt, fair value	12,963	12,935			11,792	11,751	12,327	11,156	636	636
Tax - exempt debt										$ 636