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Summary Of Significant Accounting Policies (Schedule Of Rates Used For Allowance For Funds Used During Construction) (Details)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Union Electric Company      
Accounting Policies [Line Items]      
Allowance for funds used during construction, rate 7.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
8.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
8.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Ameren Illinois Company      
Accounting Policies [Line Items]      
Allowance for funds used during construction, rate 2.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
8.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
9.00%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember