Derivative Instruments and Hedging Activities - Realized and Unrealized Gains (Losses) on Commodity Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	$ (15)	$ (38)	$ 5	$ (75)
Total deferred gains (losses)	19	(138)	69	(156)
Net deferred gains (losses)	$ 4	$ (176)	74	(231)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs	Operating costs
Pre-tax gains (losses) recognized in income
Total pre-tax gains (losses) recognized in income	$ 0	$ (1)
Regulatory Liabilities, Current
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(5)	(31)	(3)	(45)
Regulatory Liabilities, Noncurrent
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(10)	(7)	8	(30)
Regulatory Assets Current
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(9)	(18)	(14)	104
Recoverable Energy Costs, Current
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(13)	(81)	41	(269)
Regulatory Assets Non Current
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	41	(39)	42	9
CECONY | Subsidiaries
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(16)	(32)	2	(72)
Total deferred gains (losses)	12	(124)	58	(136)
Net deferred gains (losses)	(4)	(156)	60	(208)
Pre-tax gains (losses) recognized in income
Total pre-tax gains (losses) recognized in income	0	(1)
CECONY | Regulatory Liabilities, Current | Subsidiaries
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(5)	(27)	(4)	(42)
CECONY | Regulatory Liabilities, Noncurrent | Subsidiaries
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(11)	(5)	6	(30)
CECONY | Regulatory Assets Current | Subsidiaries
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(11)	(15)	(16)	102
CECONY | Recoverable Energy Costs, Current | Subsidiaries
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	(13)	(75)	38	(247)
CECONY | Regulatory Assets Non Current | Subsidiaries
Pre-tax gains (losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains (losses)	$ 36	$ (34)	$ 36	$ 9