Estimated capital costs to comply with existing and known federal and state air emission standards.

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Number of Energy Center Scrubbers to achieve compliance with regulations

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Number Of Remediation Sites

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Plant To Be Abandoned, Net

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The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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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