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Short-Term Debt and Liquidity (Short-Term Debt outstanding) (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Short-term Debt [Line Items] |  |
Short-term debt | $ 868 | $ 536
Union Electric Company |  |
Short-term Debt [Line Items] |  |
Short-term debt | 444 | 170
Ameren Illinois Company |  |
Short-term Debt [Line Items] |  |
Short-term debt | 424 | 366
Commercial Paper |  |
Short-term Debt [Line Items] |  |
Short-term debt | 868 | 536
Commercial Paper | Parent Company |  |
Short-term Debt [Line Items] |  |
Short-term debt | 0 | 0
Commercial Paper | Union Electric Company |  |
Short-term Debt [Line Items] |  |
Short-term debt | 444 | 170
Commercial Paper | Ameren Illinois Company |  |
Short-term Debt [Line Items] |  |
Short-term debt | $ 424 | $ 366

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