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Related Party Transactions (Effects of Related-party Transactions on the Statement of Income) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | $ 2,173 | $ 2,060 | $ 5,682 | $ 5,882
Other operations and maintenance | 520 | 470 | 1,455 | 1,368
(Interest Charges)/Other Income, Net | (173) | (152) | (492) | (413)
Union Electric Company |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 1,342 | 1,237 | 3,005 | 3,101
Other operations and maintenance | 288 | 256 | 789 | 732
(Interest Charges)/Other Income, Net | (62) | (63) | (187) | (166)
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 Power Supply Agreements with Ameren Illinois | Related Party Transaction [Domain] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues |  | 2 |  | 2
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 8 | 7 | 23 | 25
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 | 2 | 1
Union Electric Company | Total Related Party Operating Revenues | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 9 | 9 | 25 | 27
Union Electric Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 3 | 1 | 7 | 1
Union Electric Company | Purchased Power | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 3 | 1 | 7 | 1
Union Electric Company | Ameren Services Support Services Agreement | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 41 | 36 | 122 | 106
Union Electric Company | Total Related Party Other Operations and Maintenance | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 41 | 36 | 122 | 106
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 | 793 | 783 | 2,559 | 2,663
Purchased Power | 169 | 200 | 474 | 679
Other operations and maintenance | 229 | 200 | 663 | 603
(Interest Charges)/Other Income, Net | (63) | (54) | (178) | (151)
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 | 2 | 1 | 2
Ameren Illinois Company | Total Related Party Operating Revenues | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Operating Revenues | 1 | 2 | 1 | 2
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power |  | 2 | 1 | 2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Transmission Services from ATXI | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 1 | 1 | 2 | 1
Ameren Illinois Company | Purchased Power | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Purchased Power | 1 | 3 | 2 | 3
Ameren Illinois Company | Ameren Services Support Services Agreement | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 38 | 33 | 115 | 101
Ameren Illinois Company | Total Related Party Other Operations and Maintenance | Related Party |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Other operations and maintenance | 38 | 33 | 115 | 103
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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