Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 15,425
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	4	$ (1)
Ending Balance	15,661
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(26)	(27)
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	4
Ending Balance	(22)	(28)
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 of $(1) for Con Edison in 2018 and 2017	1	1
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	4	(1)
OCI before reclassifications, tax	(1)	1
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(1)	(1)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	0	0
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(6)	(7)
Ending Balance	(6)	(7)
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 of $(1) for Con Edison in 2018 and 2017	0	0
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	$ 0	$ 0