Commitments And Contingencies (Environmental Matters) (Details) (USD $)	12 Months Ended
Dec. 31, 2014
EPA Clean Power Plan CO2 Proposed Reductions	30.00%
Estimated Environmental Expenditures to Comply with Clean Power Plan	$ 2,000,000,000
Manufactured Gas Plant
Accrual for environmental loss contingencies	250,000,000
Manufactured Gas Plant \| Ameren Illinois Company
Number of remediation sites	44
Loss contingency range of possible loss, minimum	250,000,000
Loss contingency range of possible loss, maximum	314,000,000
Accrual for environmental loss contingencies	250,000,000
Former Coal Ash Landfill \| Ameren Illinois Company
Loss contingency range of possible loss, minimum	500,000
Loss contingency range of possible loss, maximum	6,000,000
Accrual for environmental loss contingencies	500,000
Other Environmental \| Ameren Illinois Company
Accrual for environmental loss contingencies	700,000
Former Coal Tar Distillery \| Union Electric Company
Loss contingency range of possible loss, minimum	2,000,000
Loss contingency range of possible loss, maximum	5,000,000
Accrual for environmental loss contingencies	2,000,000
Sauget Area 2 \| Union Electric Company
Loss contingency range of possible loss, minimum	1,000,000
Loss contingency range of possible loss, maximum	2,500,000
Accrual for environmental loss contingencies	1,000,000
Substation in St Charles, Missouri \| Union Electric Company
Loss contingency range of possible loss, minimum	1,600,000
Loss contingency range of possible loss, maximum	4,500,000
Accrual for environmental loss contingencies	1,600,000
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	350,000,000
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 400,000,000

EPA Clean Power Plan CO2 Proposed Reductions

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

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

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The estimated maximum amount of possible loss from the contingency.

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