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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 | Dec. 31, 2024 | Dec. 31, 2023
Ameren Illinois |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Current regulatory liabilities |  |  | $ 79 | $ 71
Final Rate Order | Midwest Independent Transmission System Operator, Inc |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public Utilities, Approved Return on Equity, Percentage | 9.98% | 10.02% |  |
Expense recognized due to lower FERC-allowed base ROE |  |  | 2 |
Current regulatory liabilities |  |  | 12 |
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Electric |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Revenue reduction due to lower FERC-allowed base ROE |  |  | 10 |
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Ameren Illinois |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Expense recognized due to lower FERC-allowed base ROE |  |  | 1 |
Current regulatory liabilities |  |  | 8 |
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Ameren Illinois | Electric |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Revenue reduction due to lower FERC-allowed base ROE |  |  | $ 7 |

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