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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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) scrubber site	Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 792	$ 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	$ 788	782
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	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	$ 58
Manufactured Gas Plant \| Ameren Illinois Company
Loss Contingencies [Line Items]
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 58
Manufactured Gas Plant \| Ameren Illinois Company \| Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	58
Manufactured Gas Plant \| Ameren Illinois Company \| Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	108
Rush Island Energy Center \| Union Electric Company
Loss Contingencies [Line Items]
Rate Base	400
New CCR Rules Estimate
Loss Contingencies [Line Items]
Asset Retirement Obligation	48
New CCR Rules Estimate \| Union Electric Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 48