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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions | Mar. 31, 2025 USD ($) scrubber site | Dec. 31, 2024 USD ($)
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Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal CO2 emissions regulations | $ 580 |
Estimated capital costs to comply with existing and known federal MATS regulations | 320 |
Asset Retirement Obligation | 835 | $ 827
Minimum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 900 |
Maximum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | $ 1,000 |
Union Electric Company |  |
Loss Contingencies [Line Items] |  |
Number of Energy Center Scrubbers | scrubber | 2 |
Estimated capital costs to comply with existing and known federal CO2 emissions regulations | $ 580 |
Estimated capital costs to comply with existing and known federal MATS regulations | 320 |
Asset Retirement Obligation | 831 | 823
Union Electric Company | Minimum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 900 |
Union Electric Company | Maximum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 1,000 |
Ameren Illinois Company |  |
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | $ 4 | $ 4
Number of remediation sites | site | 3 |
Manufactured Gas Plant |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | $ 47 |
Manufactured Gas Plant | Ameren Illinois Company |  |
Loss Contingencies [Line Items] |  |
Number of remediation sites | site | 44 |
Accrual for environmental loss contingencies | $ 47 |
Manufactured Gas Plant | Ameren Illinois Company | Minimum |  |
Loss Contingencies [Line Items] |  |
Estimate of possible loss | 47 |
Manufactured Gas Plant | Ameren Illinois Company | Maximum |  |
Loss Contingencies [Line Items] |  |
Estimate of possible loss | 91 |
New CCR Rules Estimate |  |
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | 46 |
New CCR Rules Estimate | Union Electric Company |  |
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | $ 46 |

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