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Income Tax - Summary of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 6	$ 12	$ 42
Additions based on tax positions related to the current year	1	2	1
Additions based on tax positions of prior years	10	1	1
Reductions for tax positions of prior years	(2)	(2)	(24)
Reductions from expiration of statute of limitations	0	(4)	(2)
Settlements	(2)	(3)	(6)
Balance at end of period	13	6	12
CECONY
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	4	5	21
Additions based on tax positions related to the current year	1	2	1
Additions based on tax positions of prior years	0	1	1
Reductions for tax positions of prior years	(1)	(1)	(18)
Reductions from expiration of statute of limitations	0	0	0
Settlements	(2)	(3)	0
Balance at end of period	$ 2	$ 4	$ 5

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Amount of unrecognized tax benefits.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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