Derivative Instruments and Hedging Activities - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	$ 103
Makeup of net credit exposure with investment-grade counterparties	39
Makeup of net credit exposure independent system operators	29
Makeup of net credit exposure with commodity exchange brokers	22
Makeup of net credit exposure non-investment grade/non-rated counterparties	13
Derivative liabilities	55	$ 117
Interest Rate Swap
Investment Holdings [Line Items]
Derivative liabilities	1	$ 1
CECONY
Investment Holdings [Line Items]
Energy supply and hedging activities credit exposure total	28
Makeup of net credit exposure with investment-grade counterparties	17
Makeup of net credit exposure with commodity exchange brokers	11
Clean Energy Businesses \| Coram \| Interest Rate Swap
Investment Holdings [Line Items]
Derivative, fixed interest rate		2.0855%
Derivative liabilities	$ 0	$ 1

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Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.

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