Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting of Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/ (Liabilities)	$ (183)	$ (27)
Gross Amounts Offset	17	(1)
Net Amounts of Assets/ (Liabilities)	(166)	(28)
Margin deposits	9	7
CECONY
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/ (Liabilities)	(124)	(7)
Gross Amounts Offset	17	1
Net Amounts of Assets/ (Liabilities)	(107)	(6)
Margin deposits	8	6
Clean Energy Businesses \| Interest Rate Swap
Net fair value derivative assets/(liabilities)
Notional amount	919	499
Fair Value of Derivative Liabilities, Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(140)	(61)
Gross Amounts Offset	17	11
Net Amounts of Assets/ (Liabilities)	(123)	(50)
Fair Value of Derivative Liabilities, Current \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(7)
Fair Value of Derivative Liabilities, Current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(100)	(31)
Gross Amounts Offset	19	6
Net Amounts of Assets/ (Liabilities)	(81)	(25)
Fair Value of Derivative Liabilities, Non-current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(122)	(25)
Gross Amounts Offset	16	9
Net Amounts of Assets/ (Liabilities)	(106)	(16)
Fair Value of Derivative Liabilities, Non-current \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(34)	(6)
Fair Value of Derivative Liabilities, Non-current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(80)	(12)
Gross Amounts Offset	16	6
Net Amounts of Assets/ (Liabilities)	(64)	(6)
Fair Value of Derivative Liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(262)	(86)
Gross Amounts Offset	33	20
Net Amounts of Assets/ (Liabilities)	(229)	(66)
Fair Value of Derivative Liabilities \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(180)	(43)
Gross Amounts Offset	35	12
Net Amounts of Assets/ (Liabilities)	(145)	(31)
Fair Value of Derivative Assets, Current
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	60	43
Gross Amounts Offset	(3)	(14)
Net Amounts of Assets/ (Liabilities)	57	29
Fair Value of Derivative Assets, Current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	39	25
Gross Amounts Offset	(6)	(6)
Net Amounts of Assets/ (Liabilities)	33	19
Fair Value of Derivative Assets, Non-current
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	19	16
Gross Amounts Offset	(13)	(7)
Net Amounts of Assets/ (Liabilities)	6	9
Fair Value of Derivative Assets, Non-current \| Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	1	2
Fair Value of Derivative Assets, Non-current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	17	11
Gross Amounts Offset	(12)	(5)
Net Amounts of Assets/ (Liabilities)	5	6
Fair Value of Derivative Assets
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	79	59
Gross Amounts Offset	(16)	(21)
Net Amounts of Assets/ (Liabilities)	63	38
Fair Value of Derivative Assets \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	56	36
Gross Amounts Offset	(18)	(11)
Net Amounts of Assets/ (Liabilities)	$ 38	$ 25

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Nominal or face amount used to calculate payment on derivative.

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