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

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- Definition

Estimated capital costs to comply with preliminary court order

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Estimated operations and maintenance costs to comply with preliminary court order. [Monetary Items]

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Number Of Remediation Sites

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- Definition

Number of Energy Center Scrubbers to achieve compliance with regulations

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Number of Energy Centers Constructing Wastewater Treatment Facilities

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Number of years Clean Water Act postponed for two specific waste streams

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Waste Streams identified in Clean Water Act with Postponed Compliance Dates

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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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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	12 Months Ended
	Dec. 31, 2019 USD ($) waste_stream scrubber center site	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Asset Retirement Obligation	$ 691	$ 650	$ 644
Union Electric Company
Number of Energy Center Scrubbers \| scrubber	2
Postponement of EPA's 2015 Rule	two years
Waste Streams with Postponed Compliance Dates \| waste_stream	2
Number of Energy Centers Constructing Wastewater Treatment Facilities \| center	3
Asset Retirement Obligation	$ 687	646	640
Ameren Illinois Company
Asset Retirement Obligation	4	$ 4	$ 4
Manufactured Gas Plant
Accrual for environmental loss contingencies	$ 129
Manufactured Gas Plant \| Ameren Illinois Company
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 129
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	200
Minimum \| Union Electric Company
Estimated capital costs to comply with existing and known federal and state air emissions regulations	200
Minimum \| Coal Combustion Residuals Estimate
Estimated capital costs to comply with existing and known federal and state air emissions regulations	75
Minimum \| Manufactured Gas Plant \| Ameren Illinois Company
Loss contingency, estimate of possible loss	129
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	250
Maximum \| Union Electric Company
Estimated capital costs to comply with existing and known federal and state air emissions regulations	250
Maximum \| Coal Combustion Residuals Estimate
Estimated capital costs to comply with existing and known federal and state air emissions regulations	125
Maximum \| Manufactured Gas Plant \| Ameren Illinois Company
Loss contingency, estimate of possible loss	213
Rush Island Energy Center \| Union Electric Company
Estimated capital costs to comply with preliminary court order	1,000
Rush Island Energy Center \| Minimum \| Union Electric Company
Estimated operations and maintenance costs to comply with preliminary court order.	30
Rush Island Energy Center \| Maximum \| Union Electric Company
Estimated operations and maintenance costs to comply with preliminary court order.	50
New CCR Rules Estimate
Asset Retirement Obligation	151
New CCR Rules Estimate \| Union Electric Company
Asset Retirement Obligation	$ 151