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2413402 - Disclosure - Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)
(http://www.ameren.com/role/IncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationDetails)
TableIncome Taxes [Table]
Slicers (applies to each fact value in each table cell)
Reporting Entity [Axis]0001002910 (http://www.sec.gov/CIK)
Income Taxes [Line Items]Period [Axis]
2012-01-01 - 2012-12-31
2011-01-01 - 2011-12-31
2010-01-01 - 2010-12-31
Legal Entity [Axis]Legal Entity [Axis]Legal Entity [Axis]
Union Electric Company [Member]Ameren Illinois Company [Member]Entity [Domain]Union Electric Company [Member]Ameren Illinois Company [Member]Entity [Domain]Union Electric Company [Member]Ameren Illinois Company [Member]Entity [Domain]
Statutory federal income tax rate:
0.35  
0.35  
0.35  
0.35  
0.35  
0.35  
0.35  
0.35  
0.35  
Non-deductible impairment of goodwill
 
 
 
 
 
 
xsi:nil 
xsi:nil 
.32  
Depreciation differences
(.01) 
xsi:nil 
xsi:nil 
(.02) 
xsi:nil 
(.01) 
(.03) 
xsi:nil 
(.04) 
Amortization of investment tax credit
(.01) 
(.01) 
.01  
(.01) 
(.01) 
(.01) 
(.01) 
(.01) 
(.02) 
State tax
.03  
.06  
.05  
.03  
.05  
.04  
.03  
.05  
.08  
Reserve for uncertain tax positions
.01  
xsi:nil 
xsi:nil 
 
 
 
xsi:nil 
xsi:nil 
(.01) 
Other permanent items
 
 
 
.01 2
xsi:nil 
xsi:nil 
 
 
 
Tax credits
 
 
 
 
 
 
xsi:nil 
xsi:nil 
(.03) 
Change in federal tax law
 
 
 
 
 
 
.01 1
xsi:nil1
.03 1
Effective income tax rate
.37  
 
.40  
 
.41  
 
.36  
 
.39  
 
.37  
 
.35  
 
.39  
 
.68  
 
1: Relates to change in taxation of prescription drug benefits to retiree participants from the enactment in 2010 of the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act of 2010.
2: Permanent items are treated differently for book and tax purposes and primarily include nondeductible expenses related to lobbying and stock issuance expenses for Ameren Missouri.