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Rate And Regulatory Matters (Narrative-Illinois) (Details) - Ameren Illinois Company - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2025 | Mar. 31, 2025 | Dec. 31, 2027 | Dec. 31, 2026 | Dec. 31, 2025 | Dec. 31, 2024
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |
Annual investment in energy-efficiency programs |  | $ 126 |  |  |  |
IETL | Electric Distribution |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |
Multi-year rate plan approved revenue requirement |  |  |  |  |  | $ 1,206
Public Utilities, Approved Rate Increase (Decrease), Amount |  |  |  |  |  | $ 308
IETL | Electric Distribution | Forecast |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |
Multi-year rate plan approved revenue requirement |  |  | $ 1,421 | $ 1,367 | $ 1,287 |
Pending Rate Case | Electric Distribution | Subsequent Event |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount | $ 61 |  |  |  |  |
Public Utilities, Requested Equity Capital Structure, Percentage | 50.00% |  |  |  |  |
Pending Rate Case | Natural gas |  |  |  |  |  |
Rate And Regulatory Matters [Line Items] |  |  |  |  |  |
Public Utilities, Requested Rate Increase (Decrease), Amount |  | $ 140 |  |  |  |
Public Utilities, Requested Equity Capital Structure, Percentage |  | 52.00% |  |  |  |
Public Utilities, Requested Return on Equity, Percentage |  | 10.70% |  |  |  |
Rate Base |  | $ 3,300 |  |  |  |

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