Income Tax - Summary of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 34	$ 34	$ 9
Additions based on tax positions related to the current year	2	0	0
Additions based on tax positions of prior years	19	1	27
Reductions for tax positions of prior years	(13)	0	(2)
Reductions from expiration of statute of limitations	0	(1)	0
Settlements	0	0	0
Balance at end of period	42	34	34
CECONY
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	2	2	0
Additions based on tax positions related to the current year	2	0	0
Additions based on tax positions of prior years	19	0	2
Reductions for tax positions of prior years	(2)	0	0
Reductions from expiration of statute of limitations	0	0	0
Settlements	0	0	0
Balance at end of period	$ 21	$ 2	$ 2