Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	$ 458	$ 446
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(198)	(66)
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/(Liabilities)	(206)	(27)
Gross Amounts Offset	21	(1)
Net Amounts of Assets/ (Liabilities)	(185)	(28)
Margin deposits	6	7
Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	0	2
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(37)	(6)
CECONY
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)	429	407
Net fair value derivative assets/(liabilities)
Gross Amounts of Recognized Assets/(Liabilities)	(142)	(7)
Gross Amounts Offset	25	1
Net Amounts of Assets/ (Liabilities)	(117)	(6)
Margin deposits	6	6
Clean Energy Businesses \| Interest Rate Swap
Net fair value derivative assets/(liabilities)
Notional amount	829	499
Fair Value of Derivative Liabilities, Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(97)	(61)
Gross Amounts Offset	29	11
Net Amounts of Assets/ (Liabilities)	(68)	(50)
Fair Value of Derivative Liabilities, Current \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(5)
Fair Value of Derivative Liabilities, Current \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(66)	(31)
Gross Amounts Offset	25	6
Net Amounts of Assets/ (Liabilities)	(41)	(25)
Fair Value of Derivative Liabilities, Noncurrent
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(152)	(25)
Gross Amounts Offset	22	9
Net Amounts of Assets/ (Liabilities)	(130)	(16)
Fair Value of Derivative Liabilities, Noncurrent \| Interest Rate Swap
Fair value of derivative liabilities
Net Amounts of Assets/ (Liabilities)	(32)	(6)
Fair Value of Derivative Liabilities, Noncurrent \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(106)	(12)
Gross Amounts Offset	20	6
Net Amounts of Assets/ (Liabilities)	(86)	(6)
Fair Value of Derivative Liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(249)	(86)
Gross Amounts Offset	51	20
Net Amounts of Assets/ (Liabilities)	(198)	(66)
Fair Value of Derivative Liabilities \| CECONY
Fair value of derivative liabilities
Gross Amounts of Recognized Assets/(Liabilities)	(172)	(43)
Gross Amounts Offset	45	12
Net Amounts of Assets/ (Liabilities)	(127)	(31)
Fair Value of Derivative Assets, Current
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	37	43
Gross Amounts Offset	(24)	(14)
Net Amounts of Assets/ (Liabilities)	13	29
Fair Value of Derivative Assets, Current \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	26	25
Gross Amounts Offset	(16)	(6)
Net Amounts of Assets/ (Liabilities)	10	19
Fair Value of Derivative Assets, Noncurrent
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	6	16
Gross Amounts Offset	(6)	(7)
Net Amounts of Assets/ (Liabilities)	0	9
Fair Value of Derivative Assets, Noncurrent \| Interest Rate Swap
Fair value of derivative assets
Net Amounts of Assets/ (Liabilities)		2
Fair Value of Derivative Assets, Noncurrent \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	4	11
Gross Amounts Offset	(4)	(5)
Net Amounts of Assets/ (Liabilities)	0	6
Fair Value of Derivative Assets
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	43	59
Gross Amounts Offset	(30)	(21)
Net Amounts of Assets/ (Liabilities)	13	38
Fair Value of Derivative Assets \| CECONY
Fair value of derivative assets
Gross Amounts of Recognized Assets/(Liabilities)	30	36
Gross Amounts Offset	(20)	(11)
Net Amounts of Assets/ (Liabilities)	$ 10	$ 25

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