Income Tax - Schedule of Components of Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
State
Current	$ (12)	$ (10)	$ (2)
Deferred	96	107	103
Federal
Current	0	3	(11)
Deferred	219	310	391
Amortization of investment tax credits	(7)	(9)	(9)
Total income tax expense	296	401	472
CECONY
State
Current	22	6	37
Deferred	68	82	75
Federal
Current	185	(34)	73
Deferred	63	275	504
Amortization of investment tax credits	(3)	(3)	(4)
Total income tax expense	$ 335	$ 326	$ 685