Pension Benefits - Additional Information (Detail) $ in Millions	6 Months Ended
Jun. 30, 2015 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	$ 750
CECONY \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	697
Contributions	407
CECONY \| Non-qualified Supplemental Plan
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	$ 16

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration