Income Tax - Schedule of Components of Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
State
Current	$ (2)	$ (42)	$ 38
Deferred	103	188	93
Federal
Current	(11)	(43)	(86)
Deferred	391	604	569
Amortization of investment tax credits	(9)	(9)	(9)
Total income tax expense	472	698	605
CECONY
State
Current	37	(1)	48
Deferred	75	114	82
Federal
Current	73	59	77
Deferred	504	435	372
Amortization of investment tax credits	(4)	(4)	(5)
Total income tax expense	$ 685	$ 603	$ 574