Derivative Instruments and Hedging Activities - Fair Values of Commodity Derivatives Including Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair value of derivative assets
Net Amounts of Assets (Liabilities)	$ 818	$ 741
Net fair value derivative assets (liabilities)
Gross Amounts of Recognized Assets (Liabilities)	(74)	(105)
Gross Amounts Offset	(2)	3
Net Amounts of Assets/ (Liabilities)	(76)	(102)
CECONY | Subsidiaries
Fair value of derivative assets
Net Amounts of Assets (Liabilities)	790	712
Net fair value derivative assets (liabilities)
Gross Amounts of Recognized Assets (Liabilities)	(71)	(92)
Gross Amounts Offset	1	2
Net Amounts of Assets/ (Liabilities)	(70)	(90)
Current
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(109)	(92)
Gross Amounts Offset	39	44
Net Amounts of Assets/ (Liabilities)	(70)	(48)
Current | CECONY | Subsidiaries
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(100)	(84)
Gross Amounts Offset	36	42
Net Amounts of Assets/ (Liabilities)	(64)	(42)
Noncurrent
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(71)	(108)
Gross Amounts Offset	15	12
Net Amounts of Assets/ (Liabilities)	(56)	(96)
Noncurrent | CECONY | Subsidiaries
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(61)	(95)
Gross Amounts Offset	12	11
Net Amounts of Assets/ (Liabilities)	(49)	(84)
Total fair value of derivative liabilities
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(180)	(200)
Gross Amounts Offset	54	56
Net Amounts of Assets/ (Liabilities)	(126)	(144)
Net fair value derivative assets (liabilities)
Margin deposit liability	(3)	(4)
Total fair value of derivative liabilities | CECONY
Net fair value derivative assets (liabilities)
Margin deposit liability		(2)
Total fair value of derivative liabilities | CECONY | Subsidiaries
Fair value of derivative assets
Net Amounts of Assets (Liabilities)	1
Fair value of derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(161)	(179)
Gross Amounts Offset	48	53
Net Amounts of Assets/ (Liabilities)	(113)	(126)
Net fair value derivative assets (liabilities)
Margin deposit liability	(2)
Current
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	52	56
Gross Amounts Offset	(39)	(41)
Net Amounts of Assets (Liabilities)	13	15
Current | CECONY | Subsidiaries
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	45	51
Gross Amounts Offset	(35)	(40)
Net Amounts of Assets (Liabilities)	10	11
Noncurrent
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	54	39
Gross Amounts Offset	(17)	(12)
Net Amounts of Assets (Liabilities)	37	27
Noncurrent | CECONY | Subsidiaries
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	45	36
Gross Amounts Offset	(12)	(11)
Net Amounts of Assets (Liabilities)	33	25
Total fair value of derivative assets
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	106	95
Gross Amounts Offset	(56)	(53)
Net Amounts of Assets (Liabilities)	50	42
Total fair value of derivative assets | CECONY | Subsidiaries
Fair value of derivative assets
Gross Amounts of Recognized Assets (Liabilities)	90	87
Gross Amounts Offset	(47)	(51)
Net Amounts of Assets (Liabilities)	$ 43	$ 36