Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 13,201	$ 12,770	$ 13,061	$ 12,585
Current period OCI, net of taxes	1	1	1	6
Ending Balance	13,958	12,797	13,958	12,797
OCI before reclassifications, tax			1	(2)
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]
Current period OCI, net of taxes	1	1	1	1
Accumulated Other Comprehensive Income/(Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(34)	(40)	(34)	(45)
OCI before reclassifications, net of tax of $1 and $(2) for Con Edison in 2016 and 2015, respectively			(1)	3
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax of $(1) for Con Edison in 2016 and 2015	1	1	2	3
Current period OCI, net of taxes	1	1	1	6
Ending Balance	(33)	(39)	(33)	(39)
Accumulated Other Comprehensive Income/(Loss) | CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(9)	(11)	(9)	(11)
OCI before reclassifications, net of tax of $1 and $(2) for Con Edison in 2016 and 2015, respectively			0	0
Amounts reclassified from accumulated OCI related to pension plan liabilities, net of tax of $(1) for Con Edison in 2016 and 2015	1	1	1	1
Current period OCI, net of taxes	1	1	1	1
Ending Balance	$ (8)	$ (10)	$ (8)	$ (10)