v3.26.1
Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Effective Income Tax Rate Reconciliation, Percent [Abstract]        
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 77 $ 67 $ 165 $ 139
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 20 20 41 40
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount 18 16 33 28
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount 0 (3) (3) (5)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount (3) (1) (4) (2)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Amount (18) (23) (42) (47)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Amount (6) (1) (12) (4)
Income Tax Expense (Benefit), Total $ 52 $ 43 $ 112 $ 93
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 21.00% 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 5.00%   5.00%  
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (5.00%) (4.00%) (4.00%) (4.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent 0.00% (1.00%) 0.00% (1.00%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent (1.00%) 0.00% (1.00%) 0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Percent (0.05) (0.07) (0.05) (0.07)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Percent (0.01) (0.01) (0.02) 0
Effective Income Tax Rate Reconciliation, Percent, Total 14.00% 13.00% 14.00% 14.00%
Ameren (parent)        
Effective Income Tax Rate Reconciliation, Percent [Abstract]        
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent   5.00%   5.00%
Union Electric Company        
Effective Income Tax Rate Reconciliation, Percent [Abstract]        
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 33 $ 33 $ 50 $ 43
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 4 4 6 6
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount 16 10 21 13
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount 0 (3) (2) (4)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Amount (16) (16) (24) (19)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Amount (4) (1) (5) (2)
Income Tax Expense (Benefit), Total $ 1 $ 7 $ 4 $ 11
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 21.00% 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 3.00% 3.00% 3.00% 3.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (10.00%) (7.00%) (9.00%) (7.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent 0.00% (1.00%) (1.00%) (1.00%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Percent (0.10) (0.10) (0.10) (0.10)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Percent (0.03) (0.01) (0.02) 0
Effective Income Tax Rate Reconciliation, Percent, Total 1.00% 5.00% 2.00% 6.00%
Ameren Illinois Company        
Effective Income Tax Rate Reconciliation, Percent [Abstract]        
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 42 $ 37 $ 115 $ 103
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount 16 12 42 36
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount (1) 0 (1) 0
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Amount (2) (7) (7) (18)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Amount (2) (1) (5) (4)
Income Tax Expense (Benefit), Total $ 53 $ 41 $ 144 $ 117
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00% 21.00% 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent 7.00% 7.00% 7.00% 7.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent 0.00% 0.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amortization Of Excess Deferred Income Taxes. Percent (0.01) (0.04) (0.01) (0.04)
Effective Income Tax Rate Reconciliation, Other Adjustments, Depreciation Differences. Percent (0.01) (0.01) (0.01) 0
Effective Income Tax Rate Reconciliation, Percent, Total 26.00% 23.00% 26.00% 24.00%