Income Tax - Income Tax Reconciliation (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
STATUTORY TAX RATE
Federal	21.00%	35.00%	21.00%	35.00%
Changes in computed taxes resulting from:
State income tax	5.00%	5.00%	5.00%	4.00%
Cost of removal			1.00%	1.00%
Other plant-related items	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Renewable energy credits	(1.00%)	(1.00%)	(1.00%)	(1.00%)
TCJA deferred tax re-measurement	7.00%	0.00%	3.00%	0.00%
Amortization of excess deferred federal income taxes	(2.00%)	(0.00%)	(3.00%)	(0.00%)
Other	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Effective tax rate	28.00%	37.00%	24.00%	37.00%
CECONY
STATUTORY TAX RATE
Federal	21.00%	35.00%	21.00%	35.00%
Changes in computed taxes resulting from:
State income tax	5.00%	4.00%	5.00%	4.00%
Cost of removal			1.00%	1.00%
Other plant-related items	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Renewable energy credits	(0.00%)	(0.00%)	(0.00%)	(0.00%)
TCJA deferred tax re-measurement	0.00%	0.00%	0.00%	0.00%
Amortization of excess deferred federal income taxes	(2.00%)	(0.00%)	(3.00%)	(0.00%)
Other	(1.00%)	0.00%	(1.00%)	(1.00%)
Effective tax rate	22.00%	38.00%	22.00%	38.00%