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Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Income Taxes [Line Items]      
Federal statutory corporate income tax rate 21.00% 21.00% 21.00%
Amortization of excess deferred income taxes (8.00%) (9.00%) (7.00%)
Amortization of deferred investment tax credit 0.00% (1.00%) (1.00%)
Renewable and other tax credits (3.00%)    
State tax 5.00% 5.00% 6.00%
Stock-based compensation (1.00%) (1.00%) (1.00%)
Effective income tax rate 14.00% 15.00% 18.00%
Union Electric Company      
Income Taxes [Line Items]      
Federal statutory corporate income tax rate 21.00% 21.00% 21.00%
Amortization of excess deferred income taxes (15.00%) (16.00%) (11.00%)
Amortization of deferred investment tax credit (1.00%) (1.00%) (1.00%)
Renewable and other tax credits (7.00%)    
State tax 3.00% 3.00% 5.00%
Stock-based compensation 0.00% 0.00% 0.00%
Effective income tax rate 1.00% 7.00% 14.00%
Ameren Illinois Company      
Income Taxes [Line Items]      
Federal statutory corporate income tax rate 21.00% 21.00% 21.00%
Amortization of excess deferred income taxes (3.00%) (3.00%) (4.00%)
Amortization of deferred investment tax credit 0.00% (1.00%) 0.00%
Renewable and other tax credits 0.00%    
State tax 7.00% 7.00% 7.00%
Stock-based compensation 0.00% 0.00% 0.00%
Effective income tax rate 25.00% 24.00% 24.00%