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2414402 - 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)
Income Taxes [Line Items]Period [Axis]
2016-01-01 - 2016-12-31
2015-01-01 - 2015-12-31
2014-01-01 - 2014-12-31
Legal Entity [Axis]Legal Entity [Axis]Legal Entity [Axis]
Union Electric CompanyAmeren Illinois CompanyEntity [Domain]Union Electric CompanyAmeren Illinois CompanyEntity [Domain]Union Electric CompanyAmeren Illinois CompanyEntity [Domain]
Statutory federal income tax rate:
35.00%  
35.00%  
35.00%  
35.00%  
35.00%  
35.00%  
35.00%  
35.00%  
35.00%  
Depreciation differences
1.00%  
0.00%  
0.00%  
0.00%  
(2.00%) 
(1.00%) 
   
Amortization of deferred investment tax credit
(1.00%) 
0.00%  
0.00%  
(1.00%) 
0.00%  
(1.00%) 
(1.00%) 
0.00%  
(1.00%) 
State tax
3.00%  
5.00%  
4.00%  
3.00%  
5.00%  
5.00%  
3.00%  
6.00%  
4.00%  
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent
0.00% 1
0.00% 1
(2.00%)1
      
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent
0.00%  
0.00%  
1.00%  
      
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent
0.00%  
(2.00%) 
(1.00%) 
0.00%  
(1.00%) 
 
0.00%  
 
1.00%  
Effective income tax rate
38.00%  
 
38.00%  
 
37.00%  
 
37.00%  
 
37.00%  
 
38.00%  
 
37.00%  
 
41.00%  
 
39.00%  
 
1: (a)Reflects the adoption of new authoritative accounting guidance related to share-based compensation. See Note 1 – Summary of Significant Accounting Policies for more information.