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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, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Related Party Transaction [Line Items] |  |  |
Operating Revenues | $ 7,500 | $ 7,957 | $ 6,394
Purchased power | 1,298 | 1,547 | 606
Other operations and maintenance | 1,866 | 1,937 | 1,774
Interest Charges | 566 | 486 | 383
Ameren Missouri |  |  |
Related Party Transaction [Line Items] |  |  |
Operating Revenues | 3,859 | 4,046 | 3,353
Purchased power | 483 | 677 | 227
Other operations and maintenance | 1,003 | 1,028 | 948
Interest Charges | 227 | 213 | 137
Ameren Missouri | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Operating Revenues | 2 | 9 | 16
Ameren Missouri | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Operating Revenues | 32 | 25 | 26
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 | 1 | 1 | 1
Ameren Missouri | Total Operating Revenues | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Operating Revenues | 34 | 34 | 42
Ameren Missouri | Ameren Illinois Transmission Services From ATXI | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Purchased power | 2 | 1 | 4
Ameren Missouri | Total Purchased Power | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Purchased power | 2 | 1 | 4
Ameren Missouri | Ameren Services Support Services Agreement | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Other operations and maintenance | 148 | 150 | 147
Ameren Missouri | Total Related Party Other Operations and Maintenance | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Other operations and maintenance | 148 | 150 | 148
Ameren Missouri | Money Pool Borrowings (Advances) | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Interest Charges | 1 | 1 | 1
Ameren Illinois |  |  |
Related Party Transaction [Line Items] |  |  |
Operating Revenues | 3,482 | 3,756 | 2,895
Purchased power | 820 | 880 | 400
Other operations and maintenance | 818 | 882 | 820
Interest Charges | 204 | 168 | 164
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 | 3 | 3 | 4
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 | 5
Ameren Illinois | Total Operating Revenues | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Operating Revenues | 2 | 2 | 6
Ameren Illinois | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Purchased power | 2 | 9 | 16
Ameren Illinois | Ameren Illinois Transmission Services From ATXI | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Purchased power | 1 | 1 | 1
Ameren Illinois | Total Purchased Power | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Purchased power | 3 | 9 | 17
Ameren Illinois | Ameren Services Support Services Agreement | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Other operations and maintenance | 138 | 141 | 137
Ameren Illinois | Total Related Party Other Operations and Maintenance | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Other operations and maintenance | 141 | 144 | 141
Ameren Illinois | Money Pool Borrowings (Advances) | Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Interest Charges | $ 1 | $ 1 | $ 1

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