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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions | 3 Months Ended |
--- | --- | ---
Sep. 30, 2024 USD ($) scrubber site | Mar. 31, 2024 USD ($) | Dec. 31, 2023 USD ($)
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation | $ 817 |  | $ 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 | $ 814 |  | 787
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 | 64 |  |
Loss Contingency, Loss in Period | 44 | $ 15 |
Rush Island Energy Center Additional Mitigation Relief Proposed by Ameren Missouri | Union Electric Company | Other current liabilities |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies | 40 |  |
Rush Island Energy Center Additional Mitigation Relief Proposed by Ameren Missouri | Union Electric Company | Other Noncurrent Liabilities |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies | 24 |  |
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 | 93 |  |
New CCR Rules Estimate |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation | 47 |  |
New CCR Rules Estimate | Union Electric Company |  |  |
Loss Contingencies [Line Items] |  |  |
Asset Retirement Obligation | $ 47 |  |

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