Estimated capital costs to comply with existing and known federal and state air emissions regulations

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- Definition

Number Of Remediation Sites

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- Definition

Number of Energy Center Scrubbers to achieve compliance with regulations

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- Definition

Percentage of Rate Base Related to Carbon Dioxide Energy Centers

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- Definition

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

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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Commitments And Contingencies (Environmental Matters) (Detail) $ in Millions	Mar. 31, 2019 USD ($) scrubber site	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Percentage of Rate Base Related to Carbon Dioxide Energy Centers		16.00%
Asset Retirement Obligation	$ 653	$ 650
Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	300
Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	400
Union Electric Company
Loss Contingencies [Line Items]
Percentage of Rate Base Related to Carbon Dioxide Energy Centers		32.00%
Asset Retirement Obligation	$ 649	$ 646
Number of Energy Center Scrubbers \| scrubber	2
Union Electric Company \| Minimum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 300
Union Electric Company \| Maximum
Loss Contingencies [Line Items]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	400
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	150
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	200
Manufactured Gas Plant
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 145
Manufactured Gas Plant \| Ameren Illinois Company
Loss Contingencies [Line Items]
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 145
Manufactured Gas Plant \| Ameren Illinois Company \| Minimum
Loss Contingencies [Line Items]
Estimate of possible loss	145
Manufactured Gas Plant \| Ameren Illinois Company \| Maximum
Loss Contingencies [Line Items]
Estimate of possible loss	215
New CCR Rules Estimate
Loss Contingencies [Line Items]
Asset Retirement Obligation	131
New CCR Rules Estimate \| Union Electric Company
Loss Contingencies [Line Items]
Asset Retirement Obligation	$ 131