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Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Related Party Transaction [Line Items] |  |
Operating Revenues | $ 1,816 | $ 2,062
Other operations and maintenance | 470 | 448
(Interest Charges)/Other Income, Net | 154 | 127
Union Electric Company |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 775 | 923
Other operations and maintenance | 254 | 239
(Interest Charges)/Other Income, Net | 62 | 51
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 1 | 1
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 7 | 10
Other operations and maintenance | 1 | 1
Union Electric Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 1 | 1
Union Electric Company | Total Related Party Operating Revenues | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 7 | 10
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party |  |
Related Party Transaction [Line Items] |  |
Purchased Power | 2 | 1
Union Electric Company | Purchased Power | Related Party |  |
Related Party Transaction [Line Items] |  |
Purchased Power | 2 | 1
Union Electric Company | Ameren Services Support Services Agreement | Related Party |  |
Related Party Transaction [Line Items] |  |
Other operations and maintenance | 38 | 35
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party |  |
Related Party Transaction [Line Items] |  |
Other operations and maintenance | 38 | 35
Union Electric Company | Money pool interest | Related Party |  |
Related Party Transaction [Line Items] |  |
(Interest Charges)/Other Income, Net | (3) | 1
Ameren Illinois Company |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 1,000 | 1,101
Purchased Power | 164 | 287
Other operations and maintenance | 210 | 202
(Interest Charges)/Other Income, Net | 55 | 47
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 1 | 1
Other operations and maintenance | 1 | 2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 1 | 1
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party |  |
Related Party Transaction [Line Items] |  |
Operating Revenues | 1 | 1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party |  |
Related Party Transaction [Line Items] |  |
Purchased Power | 1 | 1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party |  |
Related Party Transaction [Line Items] |  |
Purchased Power | 1 | 1
Ameren Illinois Company | Purchased Power | Related Party |  |
Related Party Transaction [Line Items] |  |
Purchased Power | 1 | 1
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party |  |
Related Party Transaction [Line Items] |  |
Other operations and maintenance | 37 | 35
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party |  |
Related Party Transaction [Line Items] |  |
Other operations and maintenance | 37 | 37
Ameren Illinois Company | Money pool interest | Related Party |  |
Related Party Transaction [Line Items] |  |
(Interest Charges)/Other Income, Net | $ (2) | $ 1

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