Pension Benefits - Total Periodic Benefit Costs (Parenthetical) (Detail) (Pension Benefits [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in CECONY's pension obligation	$ 45

The increase (decrease) during the reporting period in the amount due to fund retirement benefits to employees, retired and disabled former employees.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

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

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