Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 14,506	$ 14,306	$ 13,201	$ 13,061	$ 14,306	$ 13,061
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	(1)	1	0	0	1
Ending Balance	14,498	14,506	13,958	13,201	14,498	13,958
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(28)	(27)	(34)	(34)	(27)	(34)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	(1)	1
Ending Balance	(27)	(28)	(33)	(34)	(27)	(33)
Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax of $1 for Con Edison in 2017 and 2016					(2)	(1)
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	1		1		2	2
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1		1		0	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	0	1	0	0	1
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7)	(7)	(9)	(9)	(7)	(9)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES			1	0
Ending Balance	(7)	$ (7)	(8)	$ (9)	(7)	(8)
CECONY | Pension Plan Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications, net of tax of $1 for Con Edison in 2017 and 2016					0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax	0		1		0	1
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 0		$ 1		$ 0	$ 1