Pension Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Pension liability	$ 2,144
Investments value	225	201
Other Nonqualified Supplemental Defined Benefit Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	289	234
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension liability	2,008
Investments value	208	183
CECONY [Member] | Other Nonqualified Supplemental Defined Benefit Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	250	199
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase to regulatory assets	2,101
Charge to OCI	17
Net loss estimated to be amortized	783
Prior service cost estimated to be amortized	4
Accumulated benefit obligation	13,454	11,004	11,911
Assumptions used in calculating net periodic benefit cost	To determine the assumed discount rate, the Companies use a model that produces a yield curve based on yields on selected highly rated (Aa or higher by either Moody’s Investors Service (Moody’s) or Standard & Poor’s) corporate bonds. Bonds with insufficient liquidity, bonds with questionable pricing information and bonds that are not representative of the overall market are excluded from consideration. For example, the bonds used in the model cannot be callable, they must have a price between 50 percent and 200 percent of the original price, the yield must lie between 1 percent and 20 percent, and the amount of the bond issue outstanding must be in excess of $50 million. The spot rates defined by the yield curve and the plan’s projected benefit payments are used to develop a weighted average discount rate.
Estimated future employer contributions	756
Increase in pension benefit obligation	800
Pension Benefits [Member] | CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase to regulatory assets	1,992
Charge to OCI	3
Net loss estimated to be amortized	740
Prior service cost estimated to be amortized	2
Accumulated benefit obligation	12,553	10,268	11,116
Estimated future employer contributions	$ 703