Other Postretirement Benefits - Additional Information (Detail) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Con Edison [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Expected contributions	$ 83
Contributions to benefit plans	34
CECONY [Member]
Schedule Of Other Postretirement Benefits [Line Items]
Expected contributions	71
Contributions to benefit plans	$ 28