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Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)
3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Income Taxes [Line Items]    
Federal statutory corporate income tax rate 21.00% 21.00%
Increases (decreases) from:    
Amortization of excess deferred taxes (7.00%) (8.00%)
Amortization of deferred investment tax credit (1.00%) 0.00%
Renewable and other tax credits (4.00%) (4.00%)
State tax 6.00% 6.00%
Depreciation differences 1.00% 1.00%
Stock-based compensation 0.00% 1.00%
Other permanent items 0.00% (1.00%)
Effective income tax rate 14.00% 14.00%
Union Electric Company    
Income Taxes [Line Items]    
Federal statutory corporate income tax rate 21.00% 21.00%
Increases (decreases) from:    
Amortization of excess deferred taxes (8.00%) (12.00%)
Amortization of deferred investment tax credit (1.00%) 0.00%
Renewable and other tax credits (7.00%) (8.00%)
State tax 4.00% 4.00%
Depreciation differences 1.00% 1.00%
Stock-based compensation 0.00% 0.00%
Other permanent items 0.00% 0.00%
Effective income tax rate 8.00% 4.00%
Ameren Illinois Company    
Income Taxes [Line Items]    
Federal statutory corporate income tax rate 21.00% 21.00%
Increases (decreases) from:    
Amortization of excess deferred taxes (3.00%) (4.00%)
Amortization of deferred investment tax credit 0.00% 0.00%
Renewable and other tax credits 0.00% 0.00%
State tax 7.00% 7.00%
Depreciation differences 1.00% 0.00%
Stock-based compensation 0.00% 0.00%
Other permanent items 0.00% 0.00%
Effective income tax rate 24.00% 24.00%