Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting of Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/ (Liabilities)	$ (23)	$ (17)
Gross Amounts Offset	(1)	0
Net Amounts of Assets/ (Liabilities)	(24)	(17)
Margin deposits	7	12
Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	2
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(6)
CECONY
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/ (Liabilities)	(7)	(14)
Gross Amounts Offset	1	(1)
Net Amounts of Assets/ (Liabilities)	(6)	(15)
Margin deposits	6	11
Fair Value of Derivative Liabilities, Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(61)	(67)
Gross Amounts Offset	11	50
Net Amounts of Assets/ (Liabilities)	(50)	(17)
Fair Value of Derivative Liabilities, Current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(31)	(26)
Gross Amounts Offset	6	14
Net Amounts of Assets/ (Liabilities)	(25)	(12)
Fair Value of Derivative Liabilities, Non-current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(19)	(43)
Gross Amounts Offset	9	5
Net Amounts of Assets/ (Liabilities)	(10)	(38)
Fair Value of Derivative Liabilities, Non-current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(12)	(36)
Gross Amounts Offset	6	4
Net Amounts of Assets/ (Liabilities)	(6)	(32)
Fair Value of Derivative Liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(80)	(110)
Gross Amounts Offset	20	55
Net Amounts of Assets/ (Liabilities)	(60)	(55)
Fair Value of Derivative Liabilities \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/ (Liabilities)	(43)	(62)
Gross Amounts Offset	12	18
Net Amounts of Assets/ (Liabilities)	(31)	(44)
Fair Value of Derivative Assets, Current
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	43	83
Gross Amounts Offset	(14)	(51)
Net Amounts of Assets/ (Liabilities)	29	32
Fair Value of Derivative Assets, Current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	25	39
Gross Amounts Offset	(6)	(15)
Net Amounts of Assets/ (Liabilities)	19	24
Fair Value of Derivative Assets, Non-current
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	14	10
Gross Amounts Offset	(7)	(4)
Net Amounts of Assets/ (Liabilities)	7	6
Fair Value of Derivative Assets, Non-current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	11	9
Gross Amounts Offset	(5)	(4)
Net Amounts of Assets/ (Liabilities)	6	5
Fair Value of Derivative Assets
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	57	93
Gross Amounts Offset	(21)	(55)
Net Amounts of Assets/ (Liabilities)	36	38
Fair Value of Derivative Assets \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/ (Liabilities)	36	48
Gross Amounts Offset	(11)	(19)
Net Amounts of Assets/ (Liabilities)	$ 25	$ 29

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