Electricity Purchase Agreements - Summary of Capacity, Energy and Other Fixed Payments (Detail) (CECONY [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Capacity, energy and other fixed payments	$ 1,164	$ 1,372	$ 1,656
Linden Cogeneration [Member]
Capacity, energy and other fixed payments	297	379	414
Indian Point [Member]
Capacity, energy and other fixed payments	204	238	524
Selkirk [Member]
Capacity, energy and other fixed payments	196	209	185
Astoria Energy [Member]
Capacity, energy and other fixed payments	181	225	223
Independence [Member]
Capacity, energy and other fixed payments	127	121	119
Brooklyn Navy Yard [Member]
Capacity, energy and other fixed payments	93	123	123
Indeck Corinth [Member]
Capacity, energy and other fixed payments	$ 66	$ 77	$ 68