Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 14,306	$ 13,061
TOTAL OTHER COMPREHENSIVE LOSS, NET OF TAXES	(1)	0
Ending Balance	14,506	13,201
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
TOTAL OTHER COMPREHENSIVE LOSS, NET OF TAXES	0	0
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(27)	(34)
Ending Balance	(28)	(34)
Accumulated OCI | CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7)	(9)
Ending Balance	(7)	(9)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	(2)	(1)
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	1	1
TOTAL OTHER COMPREHENSIVE LOSS, NET OF TAXES	(1)	0
OCI before reclassifications, tax	1	1
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(1)	(1)
Pension Plan Liabilities | CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax	0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	0	0
TOTAL OTHER COMPREHENSIVE LOSS, NET OF TAXES	$ 0	$ 0