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Consolidated Statement Of Cash Flows (Parenthetical) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Capitalized interest $ 18us-gaap_InterestPaidCapitalized $ 37us-gaap_InterestPaidCapitalized $ 30us-gaap_InterestPaidCapitalized
Union Electric Company      
Capitalized interest 16us-gaap_InterestPaidCapitalized
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember		 16us-gaap_InterestPaidCapitalized
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember		 15us-gaap_InterestPaidCapitalized
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Ameren Illinois Company      
Capitalized interest $ 2us-gaap_InterestPaidCapitalized
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember		 $ 4us-gaap_InterestPaidCapitalized
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember		 $ 2us-gaap_InterestPaidCapitalized
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember