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Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Taxes [Line Items]      
Federal statutory corporate income tax rate: 21.00% 21.00% 35.00%
Amortization of excess deferred income taxes (7.00%) (4.00%)  
Amortization of deferred investment tax credit (1.00%) (1.00%) (1.00%)
State tax 6.00% 6.00% 6.00%
Stock-based compensation (1.00%)    
Other depreciation differences   0.00% 0.00%
TCJA   1.00% 14.00%
Tax Credits   0.00% 0.00%
Other permanent items   (1.00%) (2.00%)
Effective income tax rate 18.00% 22.00% 52.00%
Union Electric Company      
Income Taxes [Line Items]      
Federal statutory corporate income tax rate: 21.00% 21.00% 35.00%
Amortization of excess deferred income taxes (11.00%) (4.00%)  
Amortization of deferred investment tax credit (1.00%) (1.00%) (1.00%)
State tax 5.00% 4.00% 4.00%
Stock-based compensation 0.00%    
Other depreciation differences   0.00% 1.00%
TCJA   1.00% 6.00%
Tax Credits   (1.00%) (1.00%)
Other permanent items   0.00% 0.00%
Effective income tax rate 14.00% 20.00% 44.00%
Ameren Illinois Company      
Income Taxes [Line Items]      
Federal statutory corporate income tax rate: 21.00% 21.00% 35.00%
Amortization of excess deferred income taxes (4.00%) (4.00%)  
Amortization of deferred investment tax credit 0.00% 0.00% 0.00%
State tax 7.00% 7.00% 6.00%
Stock-based compensation 0.00%    
Other depreciation differences   (1.00%) (1.00%)
TCJA   1.00% (1.00%)
Tax Credits   0.00% 0.00%
Other permanent items     (1.00%)
Effective income tax rate 24.00% 24.00% 38.00%