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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions | Jun. 30, 2024 USD ($) scrubber site | May 30, 2024 USD ($) | Dec. 31, 2023 USD ($)
--- | --- | --- | ---
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation | $ 810 |  | $ 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 | $ 807 |  | 787
Union Electric Company | Coal Fired Electric Generation Equipment |  |  |
Loss Contingencies [Line Items] |  |  |
Plant To Be Abandoned, Net | 508 |  |
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 |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss |  | $ 120 |
Manufactured Gas Plant |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies | 45 |  |
Manufactured Gas Plant | Ameren Illinois Company |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies | $ 45 |  |
Number of remediation sites | site | 44 |  |
Manufactured Gas Plant | Ameren Illinois Company | Minimum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss | $ 45 |  |
Manufactured Gas Plant | Ameren Illinois Company | Maximum |  |  |
Loss Contingencies [Line Items] |  |  |
Estimate of possible loss | 95 |  |
New CCR Rules Estimate |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation | 42 |  |
New CCR Rules Estimate | Union Electric Company |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation | $ 42 |  |

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