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Related Party Transactions (Schedule of Capital Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Ameren Missouri |  |  |
Related Party Transaction [Line Items] |  |  |
Capital contribution from parent | $ 28 | $ 476 | $ 0
Ameren Illinois |  |  |
Related Party Transaction [Line Items] |  |  |
Capital contribution from parent | $ 2 | $ 36 | $ 91

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