Commitments And Contingencies (Environmental Matters) (Details) $ in Millions	Dec. 31, 2016 USD ($) site	Sep. 30, 2016 scrubber
Percentage of Rate Base Related to Carbon Dioxide Energy Centers	18.00%
Union Electric Company
Percentage of Rate Base Related to Carbon Dioxide Energy Centers	34.00%
Number of Energy Center Scrubbers \| scrubber		2
Manufactured Gas Plant
Accrual for environmental loss contingencies	$ 200.0
Manufactured Gas Plant \| Ameren Illinois Company
Number of remediation sites \| site	44
Accrual for environmental loss contingencies	$ 200.0
Sauget Area 2 \| Union Electric Company
Accrual for environmental loss contingencies	1.0
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	425.0
Minimum \| Manufactured Gas Plant \| Ameren Illinois Company
Loss contingency, estimate of possible loss	200.0
Minimum \| Sauget Area 2 \| Union Electric Company
Loss contingency, estimate of possible loss	1.0
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	525.0
Maximum \| Manufactured Gas Plant \| Ameren Illinois Company
Loss contingency, estimate of possible loss	268.0
Maximum \| Sauget Area 2 \| Union Electric Company
Loss contingency, estimate of possible loss	$ 2.5

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

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Number Of Remediation Sites

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Number of Energy Center Scrubbers to achieve compliance with regulations

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
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