Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 Contract
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 164
Makeup of net credit exposure with investment-grade counterparties	33
Makeup of net credit exposure with commodity exchange brokers	46
Makeup of net credit exposure independent system operators	84
Makeup of net credit exposure non-investment grade/non-rated counterparties	1
Number of Capacity Contracts	1,116
Terminate date of interest rate swap	October 2014
Interest Rate Swap [Member]
Investment Holdings [Line Items]
Derivative, fixed interest rate	6.09%
Unrealized gain (loss) on derivatives	2
Increase in the fair value of derivative	4
CECONY [Member]
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	20
Makeup of net credit exposure with investment-grade counterparties	3
Makeup of net credit exposure with commodity exchange brokers	$ 17
Number of Capacity Contracts	547