Pension Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended				12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Other nonqualified supplemental defined benefit pension [Member]	Dec. 31, 2011 Other nonqualified supplemental defined benefit pension [Member]	Dec. 31, 2012 CECONY [Member]	Dec. 31, 2011 CECONY [Member]	Dec. 31, 2012 CECONY [Member] Other nonqualified supplemental defined benefit pension [Member]	Dec. 31, 2011 CECONY [Member] Other nonqualified supplemental defined benefit pension [Member]	Dec. 31, 2012 Pension benefits [Member]	Dec. 31, 2011 Pension benefits [Member]	Dec. 31, 2010 Pension benefits [Member]	Dec. 31, 2012 Pension benefits [Member] CECONY [Member]	Dec. 31, 2011 Pension benefits [Member] CECONY [Member]	Dec. 31, 2010 Pension benefits [Member] CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension liability	$ 246	$ 238
Increase to regulatory assets	233								225
Debit to OCI	1								1
Net loss estimated to be amortized					792				837
Prior service cost estimated to be amortized					4				5
Investments value	164	129			148	120
Accumulated benefit obligation			231	208			193	171	11,911	10,595	9,319	11,116	9,876	8,694
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 and 200, 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									$ 893			$ 834