Pension Benefits - Total Periodic Benefit Costs (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	$ 227us-gaap_DefinedBenefitPlanServiceCost	$ 267us-gaap_DefinedBenefitPlanServiceCost	$ 237us-gaap_DefinedBenefitPlanServiceCost
Interest cost on projected benefit obligation	572us-gaap_DefinedBenefitPlanInterestCost	537us-gaap_DefinedBenefitPlanInterestCost	547us-gaap_DefinedBenefitPlanInterestCost
Expected return on plan assets	(832)	(750)	(705)
Recognition of net actuarial loss	618	832	709
Recognition of prior service costs	4	5	8
NET PERIODIC BENEFIT COST	589	891	796
Amortization of regulatory asset	2us-gaap_AmortizationOfRegulatoryAsset	2us-gaap_AmortizationOfRegulatoryAsset	2us-gaap_AmortizationOfRegulatoryAsset
TOTAL PERIODIC BENEFIT COST	591	893	798
Cost capitalized	(225)ed_DefinedBenefitPlanCostCapitalized	(348)ed_DefinedBenefitPlanCostCapitalized	(277)ed_DefinedBenefitPlanCostCapitalized
Reconciliation to rate level	118ed_EffectOfReconciliationToRateLevel	(84)ed_EffectOfReconciliationToRateLevel	(8)ed_EffectOfReconciliationToRateLevel
Cost charged to operating expenses	484	461	513
CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	211	249	220
Interest cost on projected benefit obligation	536	503	513
Expected return on plan assets	(789)	(713)	(670)
Recognition of net actuarial loss	586	788	670
Recognition of prior service costs	2	4	6
NET PERIODIC BENEFIT COST	546	831	739
Amortization of regulatory asset	2	2	2
TOTAL PERIODIC BENEFIT COST	548	833	741
Cost capitalized	(212)	(327)	(260)
Reconciliation to rate level	108	(87)	(12)
Cost charged to operating expenses	$ 444	$ 419	$ 469

Defined Benefit Plan Cost Capitalized

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- Definition

Defined Benefit Plan Cost Charged To Operating Expenses

+ References

No definition available.

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- Definition

Effect of Reconciliation to Rate Level

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No definition available.

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- Definition

Total Periodic Benefit Cost After Amortization of Regulatory Asset

+ References

No definition available.

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- Definition

The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.3)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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- Definition

The amount of gains or losses recognized in net periodic benefit cost.

+ References

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

+ References

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512136

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Expected Return on Plan Assets

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(3)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

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.

+ References

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

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- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(1)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Service Cost (Component of Net Periodic Pension Cost)

-URI http://asc.fasb.org/extlink&oid=6525008

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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