Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Contract
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 236
Makeup of net credit exposure independent system operators	96
Makeup of net credit exposure with commodity exchange brokers	78
Makeup of net credit exposure with investment-grade counterparties	60
Makeup of net credit exposure non-investment grade/non-rated counterparties	2
Number of contracts	1,165
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)
CECONY [Member]
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	48
Makeup of net credit exposure with commodity exchange brokers	28
Makeup of net credit exposure with investment-grade counterparties	$ 20
Number of contracts	538