Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance			$ 15,425
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 2	$ 1	8	$ 1
Ending Balance	15,898		15,898
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(20)	(27)	(26)	(27)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES			8
Ending Balance	(18)	(26)	(18)	(26)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax of $(1) and $1 for Con Edison in 2018 and 2017, respectively			3	(2)
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	2	1	5	3
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	2	1	8	1
OCI before reclassifications, tax			(1)	1
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(1)	(1)	(2)	(2)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	0	1	1	1
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(5)	(7)	(6)	(7)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES			1
Ending Balance	(5)	(6)	(5)	(6)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax of $(1) and $1 for Con Edison in 2018 and 2017, respectively			0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	0	1	1	1
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 0	$ 1	$ 1	$ 1