Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	$ 13,061	$ 12,585	$ 12,245
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	7	11	(20)
BALANCE AS OF END OF PERIOD	14,306	13,061	12,585
OCI before reclassifications, tax	(1)	(3)
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(34)	(45)	(25)
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	7	11	(20)
BALANCE AS OF END OF PERIOD	(27)	(34)	(45)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	2	5
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	5	6
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	7	11
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(3)	(4)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	2	2	(5)
OCI before reclassifications, tax	(1)
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
BALANCE AS OF BEGINNING OF PERIOD	(9)	(11)
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	2	2	(5)
BALANCE AS OF END OF PERIOD	(7)	(9)	$ (11)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	1	1
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	1	1
TOTAL OTHER COMPREHENSIVE INCOME/(LOSS), NET OF TAXES	2	2
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	$ (1)	$ (1)