Stock-Based Compensation - Summary of Status of Stock Options (Detail) (USD $)	12 Months Ended
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Shares, Beginning Balance	481,310
Exercised, Shares	(251,460)
Forfeited, Shares	0
Outstanding Shares, Ending Balance	229,850
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 43.38
Weighted Average Exercise Price, Exercised	$ 43.75
Weighted Average Exercise Price, Forfeited	$ 0
Weighted Average Exercise Price Outstanding, Ending Balance	$ 42.99
CECONY [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Shares, Beginning Balance	381,010
Exercised, Shares	(189,660)
Forfeited, Shares	0
Outstanding Shares, Ending Balance	191,350
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 43.34
Weighted Average Exercise Price, Exercised	$ 43.68
Weighted Average Exercise Price, Forfeited	$ 0
Weighted Average Exercise Price Outstanding, Ending Balance	$ 43.00

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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-Publisher FASB

-Name Accounting Standards Codification

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-Subparagraph (c)(1)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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- Definition

Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

+ References

No definition available.

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- Definition

Number of share options (or share units) exercised during the current period.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

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-Name Accounting Standards Codification

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-Publisher SEC

-Name Regulation S-X (SX)

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