Commitments And Contingencies (Other Obligations) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Long-term Purchase Commitment [Line Items]
Other obligations	$ 6,251
Union Electric Company
Long-term Purchase Commitment [Line Items]
Other obligations	4,273
Ameren Illinois Company
Long-term Purchase Commitment [Line Items]
Other obligations	$ 1,908

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