Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting of Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/ (Liabilities)	$ (366)	$ (183)
Gross Amounts Offset	3	17
Net Amounts of Assets/ (Liabilities)	(363)	(166)
Margin deposits	3	9
CECONY
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/ (Liabilities)	(252)	(124)
Gross Amounts Offset	0	17
Net Amounts of Assets/ (Liabilities)	(252)	(107)
Margin deposits	3	8
Clean Energy Businesses \| Interest Rate Swap
Net fair value derivative assets/(liabilities)
Notional amount	863	919
Fair Value of Derivative Liabilities, Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(225)	(140)
Gross Amounts Offset	(13)	17
Net Amounts of Assets/ (Liabilities)	(238)	(123)
Fair Value of Derivative Liabilities, Current \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(24)	(7)
Fair Value of Derivative Liabilities, Current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(174)	(100)
Gross Amounts Offset	11	19
Net Amounts of Assets/ (Liabilities)	(163)	(81)
Fair Value of Derivative Liabilities, Non-current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(207)	(122)
Gross Amounts Offset	(33)	16
Net Amounts of Assets/ (Liabilities)	(240)	(106)
Fair Value of Derivative Liabilities, Non-current \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(82)	(34)
Fair Value of Derivative Liabilities, Non-current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(114)	(80)
Gross Amounts Offset	9	16
Net Amounts of Assets/ (Liabilities)	(105)	(64)
Fair Value of Derivative Liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(432)	(262)
Gross Amounts Offset	(46)	33
Net Amounts of Assets/ (Liabilities)	(478)	(229)
Fair Value of Derivative Liabilities \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(288)	(180)
Gross Amounts Offset	20	35
Net Amounts of Assets/ (Liabilities)	(268)	(145)
Fair Value of Derivative Assets, Current
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	44	60
Gross Amounts Offset	14	(3)
Net Amounts of Assets/ (Liabilities)	58	57
Fair Value of Derivative Assets, Current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	20	39
Gross Amounts Offset	(12)	(6)
Net Amounts of Assets/ (Liabilities)	8	33
Fair Value of Derivative Assets, Non-current
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	22	19
Gross Amounts Offset	35	(13)
Net Amounts of Assets/ (Liabilities)	57	6
Fair Value of Derivative Assets, Non-current \| Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)		1
Fair Value of Derivative Assets, Non-current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	16	17
Gross Amounts Offset	(8)	(12)
Net Amounts of Assets/ (Liabilities)	8	5
Fair Value of Derivative Assets
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	66	79
Gross Amounts Offset	49	(16)
Net Amounts of Assets/ (Liabilities)	115	63
Fair Value of Derivative Assets \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	36	56
Gross Amounts Offset	(20)	(18)
Net Amounts of Assets/ (Liabilities)	$ 16	$ 38

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Nominal or face amount used to calculate payment on derivative.

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