Derivative Instruments and Hedging Activities - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 154
Makeup of net credit exposure non-investment grade/non-rated counterparties	50
Makeup of net credit exposure independent system operators	58
Makeup of net credit exposure with investment-grade counterparties	35
Makeup of net credit exposure with commodity exchange brokers	11
CECONY
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	6
Makeup of net credit exposure with commodity exchange brokers	$ 6