Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair value of derivative assets
Net Amounts of Assets (Liabilities)	$ 743	$ 723
Net fair value derivative assets (liabilities)
Gross Amounts of Recognized Assets (Liabilities)	(198)	(224)
Gross Amounts Offset	8	18
Net Amounts of Assets/ (Liabilities)	(190)	(206)
CECONY | Subsidiaries
Fair value of derivative assets
Net Amounts of Assets (Liabilities)	717	699
Net fair value derivative assets (liabilities)
Gross Amounts of Recognized Assets (Liabilities)	(176)	(202)
Gross Amounts Offset	7	17
Net Amounts of Assets/ (Liabilities)	(169)	(185)
Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(159)	(230)
Gross Amounts Offset	57	52
Net Amounts of Assets/ (Liabilities)	(102)	(178)
Current | CECONY | Subsidiaries
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(147)	(217)
Gross Amounts Offset	54	48
Net Amounts of Assets/ (Liabilities)	(93)	(169)
Noncurrent
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(147)	(154)
Gross Amounts Offset	27	33
Net Amounts of Assets/ (Liabilities)	(120)	(121)
Noncurrent | CECONY | Subsidiaries
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(131)	(139)
Gross Amounts Offset	25	31
Net Amounts of Assets/ (Liabilities)	(106)	(108)
Total fair value of derivative liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(306)	(384)
Gross Amounts Offset	84	85
Net Amounts of Assets/ (Liabilities)	(222)	(299)
Net fair value derivative assets (liabilities)
Margin deposit liability	(7)	(15)
Total fair value of derivative liabilities | CECONY
Net fair value derivative assets (liabilities)
Margin deposit liability		(10)
Total fair value of derivative liabilities | CECONY | Subsidiaries
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(278)	(356)
Gross Amounts Offset	79	79
Net Amounts of Assets/ (Liabilities)	(199)	(277)
Net fair value derivative assets (liabilities)
Margin deposit liability	(2)
Current
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	64	83
Gross Amounts Offset	(53)	(38)
Net Amounts of Assets (Liabilities)	11	45
Current | CECONY | Subsidiaries
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	60	78
Gross Amounts Offset	(50)	(35)
Net Amounts of Assets (Liabilities)	10	43
Noncurrent
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	44	77
Gross Amounts Offset	(23)	(29)
Net Amounts of Assets (Liabilities)	21	48
Noncurrent | CECONY | Subsidiaries
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	42	76
Gross Amounts Offset	(22)	(27)
Net Amounts of Assets (Liabilities)	20	49
Total fair value of derivative assets
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	108	160
Gross Amounts Offset	(76)	(67)
Net Amounts of Assets (Liabilities)	32	93
Net fair value derivative assets (liabilities)
Margin deposits assets	4	7
Total fair value of derivative assets | CECONY
Net fair value derivative assets (liabilities)
Margin deposits assets		6
Total fair value of derivative assets | CECONY | Subsidiaries
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	102	154
Gross Amounts Offset	(72)	(62)
Net Amounts of Assets (Liabilities)	30	$ 92
Net fair value derivative assets (liabilities)
Margin deposits assets	$ 3