Pension Benefits - Schedule of Funded Status (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CHANGE IN PROJECTED BENEFIT OBLIGATION
Benefit obligation at beginning of year	$ 12,197	$ 13,406	$ 11,825
Service cost - excluding administrative expenses	221	259	224
Interest cost on projected benefit obligation	572us-gaap_DefinedBenefitPlanInterestCost	537us-gaap_DefinedBenefitPlanInterestCost	547us-gaap_DefinedBenefitPlanInterestCost
Net actuarial (gain)/loss	2,641	(1,469)	1,323
Plan amendments	6
Benefits paid	(556)us-gaap_DefinedBenefitPlanBenefitsPaid	(536)us-gaap_DefinedBenefitPlanBenefitsPaid	(513)us-gaap_DefinedBenefitPlanBenefitsPaid
BENEFIT OBLIGATION AT END OF YEAR	15,081	12,197	13,406
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	10,755	9,135	7,800
Actual return on plan assets	752	1,310	1,094
Employer contributions	578	879	785
Benefits paid	(556)us-gaap_DefinedBenefitPlanBenefitsPaid	(536)us-gaap_DefinedBenefitPlanBenefitsPaid	(513)us-gaap_DefinedBenefitPlanBenefitsPaid
Administrative expenses	(34)	(33)	(31)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	11,495	10,755	9,135
FUNDED STATUS	(3,586)	(1,442)	(4,271)
Unrecognized net loss	4,888	2,759	5,594
Unrecognized prior service costs	20	17	23
Accumulated benefit obligation	13,454	11,004	11,911
CECONY [Member]
CHANGE IN PROJECTED BENEFIT OBLIGATION
Benefit obligation at beginning of year	11,429	12,572	11,072
Service cost - excluding administrative expenses	206	241	209
Interest cost on projected benefit obligation	536	503	513
Net actuarial (gain)/loss	2,484	(1,388)	1,255
Benefits paid	(518)	(499)	(477)
BENEFIT OBLIGATION AT END OF YEAR	14,137	11,429	12,572
CHANGE IN PLAN ASSETS
Fair value of plan assets at beginning of year	10,197	8,668	7,406
Actual return on plan assets	715	1,241	1,040
Employer contributions	535	819	729
Benefits paid	(518)	(499)	(477)
Administrative expenses	(32)	(32)	(30)
FAIR VALUE OF PLAN ASSETS AT END OF YEAR	10,897	10,197	8,668
FUNDED STATUS	(3,240)	(1,232)	(3,904)
Unrecognized net loss	4,616	2,617	5,297
Unrecognized prior service costs	4	6	10
Accumulated benefit obligation	$ 12,553	$ 10,268	$ 11,116

Defined Benefit Plan, Administrative expenses

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Defined Benefit Plan Service Cost Excluding Administrative Expenses

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Defined Benefit Plan, Unrecognized net loss

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Defined Benefit Plan, Unrecognized prior service costs

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For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

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The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The amount of increase or decrease due to a change in the terms of an existing plan or the initiation of a new plan. A plan amendment may increase or decrease benefits, including those attributed to years of service already rendered.

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