Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 14,498	$ 14,506	$ 14,306	$ 13,958	$ 13,201	$ 13,061	$ 14,306	$ 13,061
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	1	(1)	1	1	0	1	2
Ending Balance	15,110	14,498	14,506	14,275	13,958	13,201	15,110	14,275
Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(27)	(28)	(27)	(33)	(34)	(34)	(27)	(34)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	1	(1)	1	1
Ending Balance	(26)	(27)	(28)	(32)	(33)	(34)	(26)	(32)
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			3	3
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1			1			1	2
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	1	0	0	0	1	0	1	1
CECONY | Accumulated OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7)		(7)	(8)		(9)	(7)	(9)
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	1	0	$ 0	0	1	$ 0
Ending Balance	(6)	$ (7)		(8)	$ (8)		(6)	(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	1			0			1	1
TOTAL OTHER COMPREHENSIVE INCOME, NET OF TAXES	$ 1			$ 0			$ 1	$ 1