Summary of Significant Accounting Policies - Schedule of Total Excise Taxes Recorded in Operating Revenues (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Excise Taxes [Line Items]
Excise taxes	$ 365us-gaap_ExciseTaxesCollected	$ 354us-gaap_ExciseTaxesCollected	$ 334us-gaap_ExciseTaxesCollected
CECONY [Member]
Schedule of Excise Taxes [Line Items]
Excise taxes	$ 343	$ 329	$ 306

The excise taxes collected by a public utility and reported in revenues if the amount of excise taxes is equal to 1 percent or more of such total.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph e

-Article 5

Name:	us-gaap_ExciseTaxesCollected
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration