Electricity Purchase Agreements - Summary of Significant Terms of Electricity Purchase Agreements (Detail) (CECONY [Member])	12 Months Ended
	Dec. 31, 2014 MW
Brooklyn Navy Yard [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	322
Contracted Output (MW)	291
Contract Start Date	November 1996
Contract Term (Years)	40 years
Linden Cogeneration [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	1,035
Contracted Output (MW)	607
Contract Start Date	May 1992
Contract Term (Years)	25 years
Indeck Corinth [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	147
Contracted Output (MW)	131
Contract Start Date	July 1995
Contract Term (Years)	20 years
Indian Point [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	2,311
Contracted Output (MW)	500
Contract Start Date	August 2001
Contract Term (Years)	16 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