Pension Benefits - Actuarial Assumptions (Detail) (Pension benefits [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Discount rate, benefit obligations	4.10%	4.70%	5.60%
Discount rate, net periodic benefit	4.70%	5.60%	6.05%
Expected return on plan assets	8.00%	8.50%	8.50%
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	4.35%	4.35%	4.35%
Rate of compensation increase	4.35%	4.35%	4.00%
O & R [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	4.25%	4.25%	4.25%
Rate of compensation increase	4.25%	4.25%	4.00%