Commitments And Contingencies (Environmental Matters) (Details) $ in Millions	Dec. 31, 2015 USD ($) site
Manufactured Gas Plant
Accrual for environmental loss contingencies	$ 232.0
Manufactured Gas Plant \| Ameren Illinois Company
Number of remediation sites \| site	44
Loss contingency range of possible loss, minimum	$ 232.0
Loss contingency range of possible loss, maximum	313.0
Accrual for environmental loss contingencies	232.0
Former Coal Ash Landfill \| Ameren Illinois Company
Loss contingency range of possible loss, minimum	0.5
Loss contingency range of possible loss, maximum	6.0
Accrual for environmental loss contingencies	0.5
Other Environmental \| Ameren Illinois Company
Accrual for environmental loss contingencies	0.7
Former Coal Tar Distillery \| Union Electric Company
Loss contingency range of possible loss, minimum	2.0
Loss contingency range of possible loss, maximum	5.0
Accrual for environmental loss contingencies	2.0
Sauget Area 2 \| Union Electric Company
Loss contingency range of possible loss, minimum	1.0
Loss contingency range of possible loss, maximum	2.5
Accrual for environmental loss contingencies	1.0
Substation in St Charles, Missouri \| Union Electric Company
Accrual for environmental loss contingencies	0.6
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	600.0
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 700.0

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

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- Definition

Number Of Remediation Sites

+ References

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- Definition

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
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- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

The estimated minimum amount of possible loss from the contingency.

+ References

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