Electricity Purchase Agreements - Summary of Capacity, Energy and Other Fixed Payments (Details) - CECONY - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	$ 139	$ 231	$ 318
Indian Point
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	0	0	6
Astoria Generating Company
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	26	116	179
Brooklyn Navy Yard
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	113	115	124
Cogen Technologies
Long-term Contract for Purchase of Electric Power [Line Items]
Capacity, energy and other fixed payments	$ 0	$ 0	$ 9