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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, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | $ 1,693 | $ 1,760 | $ 3,509 | $ 3,822
Other operations and maintenance | 465 | 450 | 935 | 898
(Interest Charges)/Other Income, Net | (165) | (134) | (319) | (261)
Union Electric Company |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 888 | 941 | 1,663 | 1,864
Other operations and maintenance | 247 | 237 | 501 | 476
(Interest Charges)/Other Income, Net | (63) | (52) | (125) | (103)
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 1 | 1 | 1 | 1
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 8 | 8 | 15 | 18
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 | 1 | 1 | 1 | 1
Union Electric Company | Total Related Party Operating Revenues | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 9 | 8 | 16 | 18
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 2 | 1 | 4 | 1
Union Electric Company | Purchased Power | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 2 | 1 | 4 | 1
Union Electric Company | Ameren Services Support Services Agreement | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 43 | 35 | 81 | 70
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 43 | 35 | 81 | 70
Union Electric Company | Money pool interest | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
(Interest Charges)/Other Income, Net | (1) | (1) | (3) | (1)
Ameren Illinois Company |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 766 | 779 | 1,766 | 1,880
Purchased Power | 141 | 192 | 305 | 479
Other operations and maintenance | 224 | 201 | 434 | 403
(Interest Charges)/Other Income, Net | (60) | (50) | (115) | (97)
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 | 1 | 1 | 2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Miscellaneous Support Services | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 1 | 1 | 1 | 1
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 1 | 1 | 1 | 1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 1 | 1 | 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 | 1 | 1
Ameren Illinois Company | Purchased Power | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 1 | 1 | 1 | 1
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 40 | 33 | 77 | 68
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 40 | 33 | 77 | 70
Ameren Illinois Company | Money pool interest | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
(Interest Charges)/Other Income, Net | $ (1) | $ (1) | $ (2) | $ (1)

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