Derivative Instruments and Hedging Activities - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 212
Makeup of net credit exposure with commodity exchange brokers	146
Makeup of net credit exposure independent system operators	50
Makeup of net credit exposure with investment-grade counterparties	8
Makeup of net credit exposure non-investment grade/non-rated counterparties	8
CECONY
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 26