Income Tax - Summary of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 13	$ 6	$ 12
Additions based on tax positions related to the current year	0	1	2
Additions based on tax positions of prior years	1	10	1
Reductions for tax positions of prior years	0	(2)	(2)
Reductions from expiration of statute of limitations	0	0	(4)
Settlements	0	(2)	(3)
Balance at end of period	14	13	6
CECONY
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	2	4	5
Additions based on tax positions related to the current year	0	1	2
Additions based on tax positions of prior years	1	0	1
Reductions for tax positions of prior years	0	(1)	(1)
Reductions from expiration of statute of limitations	0	0	0
Settlements	0	(2)	(3)
Balance at end of period	$ 3	$ 2	$ 4