Income Tax - Income Tax Reconciliation (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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%	3.00%	5.00%	4.00%
Cost of removal	2.00%	3.00%	1.00%	2.00%
Other plant-related items	(1.00%)	(2.00%)	(1.00%)	(1.00%)
Change in deferred taxes			0.00%	(1.00%)
Renewable energy credits	(3.00%)	(2.00%)	(2.00%)	(1.00%)
Amortization of excess deferred federal income taxes	(7.00%)	(0.00%)	(4.00%)	(0.00%)
Other	0.00%	0.00%	0.00%	(1.00%)
Effective tax rate	17.00%	37.00%	20.00%	37.00%
CECONY
STATUTORY TAX RATE
Federal	21.00%	35.00%	21.00%	35.00%
Changes in computed taxes resulting from:
State income tax	4.00%	3.00%	5.00%	4.00%
Cost of removal	2.00%	3.00%	1.00%	2.00%
Other plant-related items	(1.00%)	(2.00%)	(1.00%)	(1.00%)
Change in deferred taxes			0.00%	0.00%
Renewable energy credits	(0.00%)	(0.00%)	(0.00%)	(0.00%)
Amortization of excess deferred federal income taxes	(8.00%)	(0.00%)	(4.00%)	(0.00%)
Other	(1.00%)	0.00%	0.00%	(1.00%)
Effective tax rate	17.00%	39.00%	22.00%	39.00%