Commitments And Contingencies (Other Obligations) (Detail) - Jun. 30, 2015 $ in Millions	USD ($) MWh
Long-term Purchase Commitment [Line Items]
Total Other Obligations	$ 5,110
Union Electric Company
Long-term Purchase Commitment [Line Items]
Total Other Obligations	3,247
Ameren Illinois Company
Long-term Purchase Commitment [Line Items]
Total Other Obligations	$ 1,822
Amount of Megawatthours \| MWh	5,526,000
Long-term Purchase Commitment, Amount	$ 185

Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25336-109308

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant