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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions | May 30, 2024 USD ($) | Mar. 31, 2024 USD ($) scrubber site | Dec. 31, 2023 USD ($)
--- | --- | --- | ---
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation |  | $ 798 | $ 791
Minimum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations |  | 90 |
Maximum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations |  | $ 120 |
Union Electric Company |  |  |
Loss Contingencies [Line Items] |  |  |
Number of Energy Center Scrubbers | scrubber |  | 2 |
Asset Retirement Obligation |  | $ 795 | 787
Union Electric Company | Coal Fired Electric Generation Equipment |  |  |
Loss Contingencies [Line Items] |  |  |
Plant To Be Abandoned, Net |  | 520 |
Union Electric Company | Minimum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations |  | 90 |
Union Electric Company | Maximum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations |  | 120 |
Ameren Illinois Company |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation |  | 3 | $ 4
Rush Island Energy Center Additional Mitigation Relief Proposed by Ameren Missouri | Union Electric Company |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss |  | 20 |
Accrual for environmental loss contingencies |  | 20 |
Rush Island Energy Center Additional Mitigation Relief Proposed by Department of Justice | Union Electric Company | Subsequent Event |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss | $ 120 |  |
Manufactured Gas Plant |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies |  | 46 |
Manufactured Gas Plant | Ameren Illinois Company |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies |  | $ 46 |
Number of remediation sites | site |  | 44 |
Manufactured Gas Plant | Ameren Illinois Company | Minimum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss |  | $ 46 |
Manufactured Gas Plant | Ameren Illinois Company | Maximum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss |  | 96 |
New CCR Rules Estimate |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation |  | 40 |
New CCR Rules Estimate | Union Electric Company |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation |  | $ 40 |

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