Fair Value Measurements - Reconciliation of Beginning and Ending Net Balances for Assets and Liabilities Measured at Level 3 Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (16)	$ (13)
Included in earnings	(10)	(5)
Included in regulatory assets and liabilities	(7)	18
Settlements	15	8
Transfer out of level 3	(1)	(24)
Ending Balance	(19)	(16)
CECONY
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(6)	(2)
Included in earnings	(5)	0
Included in regulatory assets and liabilities	(4)	17
Settlements	6	1
Transfer out of level 3	(1)	(22)
Ending Balance	$ (10)	$ (6)