Pension Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Pension liability	$ 968,000,000
Investments value	243,000,000	$ 225,000,000
Other Nonqualified Supplemental Defined Benefit Pension
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	285,000,000	289,000,000
CECONY
Defined Benefit Plan Disclosure [Line Items]
Pension liability	899,000,000
Investments value	221,000,000	208,000,000
CECONY | Other Nonqualified Supplemental Defined Benefit Pension
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	249,000,000	250,000,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Decrease to regulatory assets	967,000,000
Charge to OCI	10,000,000
Net loss estimated to be amortized	603,000,000
Prior service cost estimated to be amortized	4,000,000
Accumulated benefit obligation	12,909,000,000	13,454,000,000	$ 11,004,000,000
Defined benefit plan, bond amount (excess of)	50,000,000
Estimated future employer contributions	507,000,000
Increase in pension benefit obligation		800,000,000
Pension Benefits | CECONY
Defined Benefit Plan Disclosure [Line Items]
Decrease to regulatory assets	911,000,000
Charge to OCI	1,000,000
Net loss estimated to be amortized	570,000,000
Prior service cost estimated to be amortized	2,000,000
Accumulated benefit obligation	12,055,000,000	$ 12,553,000,000	$ 10,268,000,000
Estimated future employer contributions	$ 469,000,000
Minimum | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, percent of bond original price	50.00%
Defined benefit plan, bond yield (percent)	1.00%
Maximum | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, percent of bond original price	200.00%
Defined benefit plan, bond yield (percent)	20.00%