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Related Party Transactions (Schedule of Capital Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Ameren Missouri |  |  |
Related Party Transaction [Line Items] |  |  |
Capital contribution from parent | $ 0 | $ 0 | $ 207
Ameren Illinois |  |  |
Related Party Transaction [Line Items] |  |  |
Capital contribution from parent | $ 91 | $ 15 | $ 262

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