Commitments And Contingencies (Environmental Matters) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Manufactured Gas Plant
Loss contingency range of possible loss, minimum	$ 278.0
Loss contingency range of possible loss, maximum	338.0
Accrual for environmental loss contingencies	278.0	[1]
Manufactured Gas Plant | Union Electric Company
Loss contingency range of possible loss, minimum	4.0
Loss contingency range of possible loss, maximum	5.0
Accrual for environmental loss contingencies	4.0	[1]
Manufactured Gas Plant | Ameren Illinois Company
Number of remediation sites	44
Loss contingency range of possible loss, minimum	274.0
Loss contingency range of possible loss, maximum	333.0
Accrual for environmental loss contingencies	274.0	[1]
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	0.8
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	0.3
Loss contingency range of possible loss, maximum	10.0
Accrual for environmental loss contingencies	0.3
Substation in St Charles, Missouri | Union Electric Company
Loss contingency range of possible loss, minimum	1.6
Loss contingency range of possible loss, maximum	4.5
Accrual for environmental loss contingencies	1.6
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	275
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$ 350

[1] Recorded liability represents the estimated minimum probable obligations, as no other amount within the range provided a better estimate.