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Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Carrying Amount(a) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-Term Debt, Carrying Amount | $ 16,316 | $ 15,970
Debt Issuance Costs, Net | 114 | 111
Carrying Amount(a) | Union Electric Company |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-Term Debt, Carrying Amount | 6,686 | 6,341
Debt Issuance Costs, Net | 48 | 45
Carrying Amount(a) | Ameren Illinois Company |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-Term Debt, Carrying Amount | 5,233 | 5,232
Debt Issuance Costs, Net | 46 | 47
Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 14,711 | 14,833
Fair Value | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 14,258 | 14,366
Fair Value | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 453 | 467
Fair Value | Union Electric Company |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 5,923 | 5,800
Fair Value | Union Electric Company | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 5,923 | 5,800
Fair Value | Union Electric Company | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 0 | 0
Fair Value | Ameren Illinois Company |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 4,668 | 4,867
Fair Value | Ameren Illinois Company | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 4,668 | 4,867
Fair Value | Ameren Illinois Company | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | $ 0 | $ 0

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