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Fair Value Measurements (Schedule Of Transfers Between Fair Value Hierarchy Levels) (Details) (Power, USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Transfer into Level 3/Transfers out of Level 2 $ (3)aee_TransfersIntoAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel3AndTransfersOutOfAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel2
Transfers out of Level 3/Transfers into Level 2 4aee_TransfersOutOfAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel3AndTransfersIntoAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel2
Union Electric Company  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Transfer into Level 3/Transfers out of Level 2 (3)aee_TransfersIntoAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel3AndTransfersOutOfAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel2
/ us-gaap_DerivativeByNatureAxis
= aee_PowerMember
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Transfers out of Level 3/Transfers into Level 2 $ 4aee_TransfersOutOfAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel3AndTransfersIntoAssetsAndLiabilitiesClassifiedAsFairValueInputsLevel2
/ us-gaap_DerivativeByNatureAxis
= aee_PowerMember
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember