v3.26.1
Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Related Party Transaction [Line Items]        
Operating Revenues $ 2,092 $ 2,221 $ 4,268 $ 4,318
Other operations and maintenance 521 460 1,012 945
Interest Charges 209 187 413 362
Union Electric Company        
Related Party Transaction [Line Items]        
Operating Revenues 1,124 1,340 2,054 2,297
Other operations and maintenance 282 238 546 488
Interest Charges 83 70 165 130
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 11 8 21 15
Other operations and maintenance 1 1 1 1
Union Electric Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 2   2  
Union Electric Company | Total Related Party Operating Revenues | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 13 8 23 15
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 3 2 5 5
Union Electric Company | Ameren Services Support Services Agreement | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 48 44 96 88
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 48 44 96 88
Union Electric Company | Money pool interest (advances) | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 1 1 1
Union Electric Company | Long-Term Debt | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 1 2 1
Union Electric Company | Purchased Power | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 3 2 5 5
Union Electric Company | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues   1   1
Union Electric Company | Ameren Missouri Interconnection Agreement With Ameren Illinois | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 1 1 1 1
Ameren Illinois Company        
Related Party Transaction [Line Items]        
Operating Revenues 928 843 2,127 1,943
Purchased Power 193 183 415 358
Other operations and maintenance 248 225 480 461
Interest Charges 69 63 137 125
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1 1 1 1
Other operations and maintenance 1 2 1 3
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1 3 1 5
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues 1 4 1 6
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 1 1 2 1
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 46 40 90 80
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party        
Related Party Transaction [Line Items]        
Other operations and maintenance 46 42 76 83
Ameren Illinois Company | Money pool interest (advances) | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 1 1 1
Ameren Illinois Company | Long-Term Debt | Related Party        
Related Party Transaction [Line Items]        
Interest Charges 1 1 1 1
Ameren Illinois Company | Purchased Power | Related Party        
Related Party Transaction [Line Items]        
Purchased Power 1 1 2 1
Ameren Illinois Company | Ameren Illinois Interconnection Agreement With Ameren Missouri | Related Party        
Related Party Transaction [Line Items]        
Operating Revenues $ 1 $ 1 $ 1 $ 1