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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2022 USD ($) energyCenter scrubber site | Dec. 31, 2021 USD ($)
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | $ 781 | $ 764
Minimum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 125 |
Maximum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | $ 175 |
Union Electric Company |  |
Loss Contingencies [Line Items] |  |
Number of Energy Center Scrubbers | scrubber | 2 |
Number of Months of System Support Agreement | 12 months |
Number of Energy Centers Constructing Wastewater Treatment Facilities | energyCenter | 3 |
Number of energy centers | energyCenter | 4 |
Number of Days to Comply after Final EPA Determination | 135 days |
Asset Retirement Obligation | $ 777 | 760
Number of Ameren Missouri Natural Gas Energy Centers Subject To IETL | energyCenter | 4 |
Union Electric Company | Coal Fired Electric Generation Equipment |  |
Loss Contingencies [Line Items] |  |
Plant To Be Abandoned, Net | $ 600 |
Union Electric Company | Minimum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 125 |
Union Electric Company | Maximum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 175 |
Ameren Illinois Company |  |
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | 4 | $ 4
Coal Combustion Residuals Estimate | Union Electric Company | Minimum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 60 |
Coal Combustion Residuals Estimate | Union Electric Company | Maximum |  |
Loss Contingencies [Line Items] |  |
Estimated capital costs to comply with existing and known federal and state air emissions regulations | 80 |
Manufactured Gas Plant |  |
Loss Contingencies [Line Items] |  |
Accrual for environmental loss contingencies | $ 78 |
Manufactured Gas Plant | Ameren Illinois Company |  |
Loss Contingencies [Line Items] |  |
Number of remediation sites | site | 44 |
Accrual for environmental loss contingencies | $ 78 |
Manufactured Gas Plant | Ameren Illinois Company | Minimum |  |
Loss Contingencies [Line Items] |  |
Estimate of possible loss | 78 |
Manufactured Gas Plant | Ameren Illinois Company | Maximum |  |
Loss Contingencies [Line Items] |  |
Estimate of possible loss | 147 |
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 | 77 |
New CCR Rules Estimate | Union Electric Company |  |
Loss Contingencies [Line Items] |  |
Asset Retirement Obligation | $ 77 |

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