Fair Value Measurements (Schedule Of Transfers Between Fair Value Hierarchy Levels) (Detail) (Power, USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014
Derivative [Line Items]
Assets Transfers out of Level 3	$ 1
Union Electric Company
Derivative [Line Items]
Assets Transfers out of Level 3	$ 1

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

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration