Income Tax - Schedule of Components of Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
State
Current	$ 7	$ (12)	$ (10)
Deferred	50	96	107
Federal
Current	(2)	0	3
Deferred	42	219	310
Amortization of investment tax credits	(7)	(7)	(9)
Total income tax expense	90	296	401
CECONY
State
Current	6	22	6
Deferred	97	68	82
Federal
Current	41	185	(34)
Deferred	73	63	275
Amortization of investment tax credits	(2)	(3)	(3)
Total income tax expense	$ 215	$ 335	$ 326