Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	$ 506	$ 550
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(381)	(229)
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/(Liabilities)	(330)	(183)
Gross Amounts Offset	14	17
Net Amounts of Assets/ (Liabilities)	(316)	(166)
Margin deposits	8	9
Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	0	1
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(126)	(41)
CECONY
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	453	498
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/(Liabilities)	(185)	(124)
Gross Amounts Offset	11	17
Net Amounts of Assets/ (Liabilities)	(174)	(107)
Margin deposits	7	8
Clean Energy Businesses \| Interest Rate Swap
Net fair value derivative assets/(liabilities)
Notional amount	910	919
Fair Value of Derivative Liabilities, Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(167)	(140)
Gross Amounts Offset	14	17
Net Amounts of Assets/ (Liabilities)	(153)	(123)
Fair Value of Derivative Liabilities, Current \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(17)	(7)
Fair Value of Derivative Liabilities, Current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(123)	(100)
Gross Amounts Offset	24	19
Net Amounts of Assets/ (Liabilities)	(99)	(81)
Fair Value of Derivative Liabilities, Noncurrent
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(241)	(122)
Gross Amounts Offset	13	16
Net Amounts of Assets/ (Liabilities)	(228)	(106)
Fair Value of Derivative Liabilities, Noncurrent \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(109)	(34)
Fair Value of Derivative Liabilities, Noncurrent \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(122)	(80)
Gross Amounts Offset	9	16
Net Amounts of Assets/ (Liabilities)	(113)	(64)
Fair Value of Derivative Liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(408)	(262)
Gross Amounts Offset	27	33
Net Amounts of Assets/ (Liabilities)	(381)	(229)
Fair Value of Derivative Liabilities \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(245)	(180)
Gross Amounts Offset	33	35
Net Amounts of Assets/ (Liabilities)	(212)	(145)
Fair Value of Derivative Assets, Current
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	61	60
Gross Amounts Offset	(4)	(3)
Net Amounts of Assets/ (Liabilities)	57	57
Fair Value of Derivative Assets, Current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	44	39
Gross Amounts Offset	(14)	(6)
Net Amounts of Assets/ (Liabilities)	30	33
Fair Value of Derivative Assets, Noncurrent
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	17	19
Gross Amounts Offset	(9)	(13)
Net Amounts of Assets/ (Liabilities)	8	6
Fair Value of Derivative Assets, Noncurrent \| Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)		1
Fair Value of Derivative Assets, Noncurrent \| 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)	78	79
Gross Amounts Offset	(13)	(16)
Net Amounts of Assets/ (Liabilities)	65	63
Fair Value of Derivative Assets \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	60	56
Gross Amounts Offset	(22)	(18)
Net Amounts of Assets/ (Liabilities)	$ 38	$ 38

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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