Other Postretirement Benefits - Schedule of Actuarial Assumptions (Detail) (Other Postretirement Benefits [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.75%	7.75%	8.50%
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate, benefit obligations	3.75%	4.50%	3.75%
Discount rate, net periodic benefit cost	4.50%	3.75%	4.55%
O&R [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate, benefit obligations	3.85%	4.75%	4.05%
Discount rate, net periodic benefit cost	4.75%	4.05%	4.55%