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Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt Issuance Costs, Net | $ 62 | $ 62
Ameren Illinois |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt Issuance Costs, Net | 56 | 51
Carrying Amount(a) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt (including current portion) | 19,187 | 17,579
Debt Issuance Costs, Net | 136 | 129
Carrying Amount(a) | Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt (including current portion) | 8,230 | 7,745
Debt Issuance Costs, Net | 62 | 62
Carrying Amount(a) | Ameren Illinois |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt (including current portion) | 6,259 | 5,852
Debt Issuance Costs, Net | 56 | 51
Fair Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 17,992 | 15,933
Fair Value | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 17,433 | 15,395
Fair Value | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 559 | 538
Fair Value | Ameren Missouri |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 7,608 | 6,926
Fair Value | Ameren Missouri | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 7,608 | 6,926
Fair Value | Ameren Missouri | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 0 | 0
Fair Value | Ameren Illinois |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 5,753 | 5,243
Fair Value | Ameren Illinois | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | 5,753 | 5,243
Fair Value | Ameren Illinois | Level 3 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term Debt, Fair Value | $ 0 | $ 0

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