Fair Value Measurements (Schedule Of Transfers Between Fair Value Hierarchy Levels) (Detail) - Fuel Oils $ in Millions	9 Months Ended
Sep. 30, 2015 USD ($)
Derivative [Line Items]
Assets Transfers out of Level 3	$ 2
Union Electric Company
Derivative [Line Items]
Assets Transfers out of Level 3	$ 2

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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