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Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income Taxes [Line Items]      
Statutory federal income tax rate: 35.00% 35.00% 35.00%
Depreciation differences    (1.00%) (1.00%)
Amortization of investment tax credit (1.00%) (1.00%) (1.00%)
State tax 4.00% 5.00% 4.00%
Other permanent items(a)      1.00%
Other permanent items    (1.00%) [1]  
Tax credits     (1.00%)
Effective income tax rate 38.00% 37.00% 37.00%
Union Electric Company
     
Income Taxes [Line Items]      
Statutory federal income tax rate: 35.00% 35.00% 35.00%
Depreciation differences 0.00% (1.00%) (2.00%)
Amortization of investment tax credit (1.00%) (1.00%) (1.00%)
State tax 3.00% 3.00% 3.00%
Other permanent items(a)   1.00%   
Other permanent items 1.00% [1] 0.00% 1.00% [1]
Tax credits       
Effective income tax rate 38.00% 37.00% 36.00%
Ameren Illinois Company
     
Income Taxes [Line Items]      
Statutory federal income tax rate: 35.00% 35.00% 35.00%
Depreciation differences (1.00%)      
Amortization of investment tax credit 0.00% (1.00%) (1.00%)
State tax 6.00% 6.00% 5.00%
Other permanent items(a)        
Other permanent items        
Tax credits       
Effective income tax rate 40.00% 40.00% 39.00%
[1] Permanent items are treated differently for book and tax purposes and primarily include non-taxable income related to company-owned life insurance and deductions related to dividends on DRPlus and the 401(k) plan for Ameren, as well as nondeductible expenses related to lobbying and stock issuance costs for Ameren Missouri.