Electricity Purchase Agreements - Summary of Significant Terms of Electricity Purchase Agreement (Detail) (CECONY [Member])	12 Months Ended
	Dec. 31, 2012 MW
Long-term Contract for Purchase of Electric Power [Line Items]
Contracted Output (MW)	500
Indian Point [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	1,299
Contracted Output (MW)	350
Contract Start Date	August 2001
Contract Term (Years)	16 years
Independence [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	1,254
Contracted Output (MW)	697
Contract Start Date	November 1994
Contract Term (Years)	20 years
Linden Cogeneration [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	1,035
Contracted Output (MW)	628
Contract Start Date	May 1992
Contract Term (Years)	25 years
Astoria Energy [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	640
Contracted Output (MW)	500
Contract Start Date	May 2006
Contract Term (Years)	10 years
Selkirk [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	446
Contracted Output (MW)	265
Contract Start Date	September 1994
Contract Term (Years)	20 years
Brooklyn Navy Yard [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	322
Contracted Output (MW)	263
Contract Start Date	November 1996
Contract Term (Years)	40 years
Indeck Corinth [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	147
Contracted Output (MW)	132
Contract Start Date	July 1995
Contract Term (Years)	20 years