Electricity Purchase Agreements - Summary of Capacity, Energy and Other Fixed Payments (Details) - CECONY - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	$ 692	$ 865	$ 1,312
Linden Cogeneration
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	304	323	381
Indian Point
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	203	226	247
Astoria Energy
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	50	178	230
Astoria Generating Company
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	16	0	0
Brooklyn Navy Yard
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	119	113	133
Indeck Corinth
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	0	25	80
Selkirk
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	0	0	144
Independence
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	$ 0	$ 0	$ 97