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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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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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) (Details) $ in Millions	Dec. 31, 2018 USD ($) site	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 scrubber	Dec. 31, 2016 USD ($)
Percentage of Rate Base Related to Carbon Dioxide Energy Centers	17.00%
Asset Retirement Obligation	$ 650		$ 644		$ 650
Union Electric Company
Percentage of Rate Base Related to Carbon Dioxide Energy Centers	32.00%
Number of Energy Center Scrubbers \| scrubber				2
Asset Retirement Obligation	$ 646		640		644
Ameren Illinois Company
Asset Retirement Obligation	4		$ 4		$ 6
Manufactured Gas Plant
Accrual for environmental loss contingencies	$ 150
Manufactured Gas Plant \| Ameren Illinois Company
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 150
Sauget Area 2 \| Union Electric Company
Accrual for environmental loss contingencies	1
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	300
Minimum \| Coal Combustion Residuals Estimate [Member]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	150
Minimum \| Manufactured Gas Plant \| Ameren Illinois Company
Loss contingency, estimate of possible loss	150
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	400
Maximum \| Coal Combustion Residuals Estimate [Member]
Estimated capital costs to comply with existing and known federal and state air emissions regulations	200
Maximum \| Manufactured Gas Plant \| Ameren Illinois Company
Loss contingency, estimate of possible loss	212
New CCR Rules Estimate [Member]
Asset Retirement Obligation		$ 135
New CCR Rules Estimate [Member] \| Union Electric Company
Asset Retirement Obligation	$ 150