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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2023 USD ($) scrubber site | Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | $ 784 | $ 786
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 | $ 780 | 782
Union Electric Company | Coal Fired Electric Generation Equipment |  |
Loss Contingencies [Line Items] |  |
Plant To Be Abandoned, Net | 550 |
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 | 4 | $ 4
Manufactured Gas Plant |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | $ 60 |
Manufactured Gas Plant | Ameren Illinois Company |  |
Loss Contingencies [Line Items] |  |
Number of remediation sites | site | 44 |
Accrual for environmental loss contingencies | $ 60 |
Manufactured Gas Plant | Ameren Illinois Company | Minimum |  |
Loss Contingencies [Line Items] |  |
Estimate of possible loss | 60 |
Manufactured Gas Plant | Ameren Illinois Company | Maximum |  |
Loss Contingencies [Line Items] |  |
Estimate of possible loss | 112 |
Rush Island Energy Center | Union Electric Company |  |
Loss Contingencies [Line Items] |  |
Rate Base | 500 |
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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