Fair Value Measurements - Reconciliation of Assets and Liabilities Measured at Level 3 Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (17)	$ (11)	$ (15)	$ (8)
Included in earnings	2	(1)	(1)	(6)
Included in regulatory assets and liabilities	5	(15)	3	(13)
Settlements	(2)	2	1	7
Transfer out of level 3			0	(5)
Ending balance	(12)	(25)	(12)	(25)
CECONY | Subsidiaries
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(8)	(6)	(6)	(5)
Included in earnings	1	0	1	(2)
Included in regulatory assets and liabilities	1	(12)	(1)	(8)
Settlements	(1)	1	(1)	3
Transfer out of level 3			0	(5)
Ending balance	$ (7)	$ (17)	$ (7)	$ (17)