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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 |  |

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