Electricity Purchase Agreements - Summary of Estimated Capacity and Other Fixed Payments (Detail) (CECONY [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	$ 1,282	$ 1,164	$ 1,372
2014 [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	447
2015 [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	235
2016 [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	169
2017 [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	113
Year 2018 [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	57
All Years Thereafter [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Fixed payment under the contracts	$ 875