Electricity Purchase Agreements - Summary of Significant Terms of Electricity Purchase Agreements (Detail) - CECONY	12 Months Ended
	Dec. 31, 2015 MW
Brooklyn Navy Yard
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	322
Contracted Output (MW)	299
Contract Term (Years)	40 years
Linden Cogeneration
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	1,035
Contracted Output (MW)	609
Contract Term (Years)	25 years
Indian Point
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	2,311
Contracted Output (MW)	500
Contract Term (Years)	16 years
Astoria Energy
Long-term Contract for Purchase of Electric Power [Line Items]
Plant Output (MW)	640
Contracted Output (MW)	500
Contract Term (Years)	10 years