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Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Oct. 31, 2024 | May 31, 2020 | Sep. 30, 2024 | Dec. 31, 2023
Ameren Illinois Company |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |
Current regulatory liabilities |  |  | $ 50 | $ 71
Midwest Independent Transmission System Operator, Inc | Final Rate Order |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |
Approved return on equity percentage |  | 10.02% |  |
Expense recognized due to lower FERC-allowed base ROE |  |  | 2 |
Current regulatory liabilities |  |  | 12 |
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Electric |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |
Revenue reduction due to lower FERC-allowed base ROE |  |  | 10 |
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Subsequent Event |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |
Approved return on equity percentage | 9.98% |  |  |
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |
Expense recognized due to lower FERC-allowed base ROE |  |  | 1 |
Current regulatory liabilities |  |  | 8 |
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company | Electric |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |
Revenue reduction due to lower FERC-allowed base ROE |  |  | $ 7 |

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