Summary of Significant Accounting Policies - Changes in Accumulated Other Comprehensive Income/(Loss) by Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 13,061	$ 12,585
Current period OCI, net of taxes	0	5
Ending Balance	13,201	12,770
OCI before reclassifications, tax	1	(2)
Amounts reclassified from accumulated OCI related to pension plan liabilities, tax	(1)	(1)
CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Current period OCI, net of taxes	0	0
Accumulated Other Comprehensive Income/(Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(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	2
Current period OCI, net of taxes	0	5
Ending Balance	(34)	(40)
Accumulated Other Comprehensive Income/(Loss) | CECONY
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(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	0	0
Current period OCI, net of taxes	0	0
Ending Balance	$ (9)	$ (11)