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, 2013	Dec. 31, 2012	Dec. 31, 2011
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	$ 1,282	$ 1,164	$ 1,372
Linden Cogeneration [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	346	297	379
Indian Point [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	220	204	238
Selkirk [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	215	196	209
Astoria Energy [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	183	181	225
Independence [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	121	127	121
Brooklyn Navy Yard [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	118	93	123
Indeck Corinth [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	$ 79	$ 66	$ 77