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Summary Of Significant Accounting Policies (Narrative) (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Closing common share price   $ 46.13us-gaap_SharePrice
Performance Shares    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Fair value of each share unit, per share $ 52.88us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 [1]  
Performance period 3 years  
Risk free interest rate period 3 years  
Three-year risk-free rate 1.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Volatility rate, minimum 12.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Volatility rate, maximum 18.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Minimum    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Costs Incurred, Asset Retirement Obligation Incurred $ 90us-gaap_CostsIncurredAssetRetirementObligationIncurred
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Minimum | Union Electric Company    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Costs Incurred, Asset Retirement Obligation Incurred 90us-gaap_CostsIncurredAssetRetirementObligationIncurred
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maximum    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Costs Incurred, Asset Retirement Obligation Incurred 120us-gaap_CostsIncurredAssetRetirementObligationIncurred
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maximum | Union Electric Company    
Basis Of Presentation And Significant Accounting Policies [Line Items]    
Costs Incurred, Asset Retirement Obligation Incurred $ 120us-gaap_CostsIncurredAssetRetirementObligationIncurred
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
[1] Performance share units granted to certain executive and nonexecutive officers and other eligible employees in 2015 under the 2014 Incentive Plan.