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Related Party Transactions (Effects of Related-party Transactions on the Statement of Income (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Related Party Transaction [Line Items]      
Operating Revenues $ 7,623 $ 7,500 $ 7,957
Other operations and maintenance 1,969 1,866 1,937
Interest Charges 663 566 486
Ameren Missouri      
Related Party Transaction [Line Items]      
Operating Revenues 3,993 3,859 4,046
Other operations and maintenance 1,050 1,003 1,028
Interest Charges 244 227 213
Ameren Missouri | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 0 2 9
Ameren Missouri | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 31 32 25
Other operations and maintenance 1 1 1
Ameren Missouri | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 2 1 1
Ameren Missouri | Total Operating Revenues | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 33 34 34
Ameren Missouri | Ameren Illinois Transmission Services From ATXI | Related Party      
Related Party Transaction [Line Items]      
Purchased power 9 2 1
Ameren Missouri | Total Purchased Power | Related Party      
Related Party Transaction [Line Items]      
Purchased power 9 2 1
Ameren Missouri | Ameren Services Support Services Agreement | Related Party      
Related Party Transaction [Line Items]      
Other operations and maintenance 169 148 150
Ameren Missouri | Total Related Party Other Operations and Maintenance | Related Party      
Related Party Transaction [Line Items]      
Other operations and maintenance 170 148 150
Ameren Missouri | Money Pool Borrowings (Advances) | Related Party      
Related Party Transaction [Line Items]      
Interest Charges (4) 1 1
Ameren Missouri | Long-Term Debt | Related Party      
Related Party Transaction [Line Items]      
Interest Charges 1    
Ameren Illinois      
Related Party Transaction [Line Items]      
Operating Revenues 3,472 3,482 3,756
Purchased power 621 820 880
Other operations and maintenance 906 818 882
Interest Charges 241 204 168
Ameren Illinois | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 1 1 1
Other operations and maintenance 1 3 3
Ameren Illinois | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 2 2 2
Ameren Illinois | Total Operating Revenues | Related Party      
Related Party Transaction [Line Items]      
Operating Revenues 3 2 2
Ameren Illinois | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party      
Related Party Transaction [Line Items]      
Purchased power 0 2 9
Ameren Illinois | Ameren Illinois Transmission Services From ATXI | Related Party      
Related Party Transaction [Line Items]      
Purchased power 2 1  
Ameren Illinois | Total Purchased Power | Related Party      
Related Party Transaction [Line Items]      
Purchased power 2 3 9
Ameren Illinois | Ameren Services Support Services Agreement | Related Party      
Related Party Transaction [Line Items]      
Other operations and maintenance 158 138 141
Ameren Illinois | Total Related Party Other Operations and Maintenance | Related Party      
Related Party Transaction [Line Items]      
Other operations and maintenance 159 141 144
Ameren Illinois | Money Pool Borrowings (Advances) | Related Party      
Related Party Transaction [Line Items]      
Interest Charges 1 $ 1 $ 1
Ameren Illinois | Long-Term Debt | Related Party      
Related Party Transaction [Line Items]      
Interest Charges $ 1