Leases - Schedule of Capital Leases (Detail) (Common [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Leases
Utility Plant	$ 3us-gaap_CapitalLeasedAssetsGross	$ 3us-gaap_CapitalLeasedAssetsGross
CECONY [Member]
Leases
Utility Plant	$ 1	$ 2

Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735

Name:	us-gaap_CapitalLeasedAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant