Summary of Significant Accounting Policies - Schedule of Total Excise Taxes Recorded in Operating Revenues (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Excise Taxes [Line Items]
Excise taxes	$ 354	$ 365	$ 354
CECONY
Schedule of Excise Taxes [Line Items]
Excise taxes	$ 331	$ 343	$ 329

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