Derivative Instruments and Hedging Activities - Fair Values of Companies' Commodity Derivatives (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives Assets
Impact of netting	$ 84	$ 110
Derivatives Assets [Member]
Derivatives Assets
Fair value of derivative assets	86	165
Impact of netting	(20)	(95)
Net derivatives assets	66	70
Derivatives Assets [Member] \| Other current assets [Member]
Derivatives Assets
Fair value of derivative assets	64	139
Derivatives Assets [Member] \| Other deferred charges and non-current assets [Member]
Derivatives Assets
Fair value of derivative assets	22	26
Derivatives Liabilities [Member]
Derivatives Liabilities
Fair value of derivative liabilities	176	414
Impact of netting	(104)	(205)
Net derivatives liabilities	72	209
Derivatives Liabilities [Member] \| Fair value of derivative liabilities, Current [Member]
Derivatives Liabilities
Fair value of derivative liabilities	122	331
Derivatives Liabilities [Member] \| Fair value of derivative liabilities, Long-term [Member]
Derivatives Liabilities
Fair value of derivative liabilities	54	83
CECONY [Member]
Derivatives Assets
Impact of netting	47	46
CECONY [Member] \| Derivatives Assets [Member]
Derivatives Assets
Fair value of derivative assets	27	30
Impact of netting	3	(6)
Net derivatives assets	30	24
CECONY [Member] \| Derivatives Assets [Member] \| Other current assets [Member]
Derivatives Assets
Fair value of derivative assets	18	16
CECONY [Member] \| Derivatives Assets [Member] \| Other deferred charges and non-current assets [Member]
Derivatives Assets
Fair value of derivative assets	9	14
CECONY [Member] \| Derivatives Liabilities [Member]
Derivatives Liabilities
Fair value of derivative liabilities	83	175
Impact of netting	(44)	(53)
Net derivatives liabilities	39	122
CECONY [Member] \| Derivatives Liabilities [Member] \| Fair value of derivative liabilities, Current [Member]
Derivatives Liabilities
Fair value of derivative liabilities	58	127
CECONY [Member] \| Derivatives Liabilities [Member] \| Fair value of derivative liabilities, Long-term [Member]
Derivatives Liabilities
Fair value of derivative liabilities	$ 25	$ 48

Derivative Asset Not Designated As Hedging Instrument Fair Value Net After Offset Under Master Netting Agreement

No definition available.

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- Definition

Derivative Liability Not Designated As Hedging Instrument Fair Value Net After Offset Under Master Netting Agreement

+ References

No definition available.

+ Details

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Namespace Prefix:	ed_
Data Type:	xbrli:monetaryItemType
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- Definition

Fair value of the gross assets less the gross liabilities of a derivative asset or group of derivative assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611

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- Definition

The amount as of the balance sheet date of the fair value of derivative assets that in accordance with the entity's accounting policy was offset against an obligation to return cash collateral under a master netting arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41678-113959

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FIN39-1

-Paragraph 10B

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

The amount as of the balance sheet date of the fair value of derivative liabilities that in accordance with the entity's accounting policy were offset against the right to reclaim cash collateral under a master netting arrangement.

+ References

+ Details

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- Definition

Fair value of the gross liabilities less the gross assets of a derivative liability or group of derivative liabilities.

+ References

+ Details

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