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Summary Of Significant Accounting Policies (Tables)
9 Months Ended
Sep. 30, 2011
Summary Of Significant Accounting Policies [Abstract] 
Schedule Of Amortization Expense For Intangible Assets
      Three Months     Nine Months  
      2011     2010     2011     2010  

Ameren(a)

    $ (b )    $ 10      $ 2      $ 20   

Ameren Missouri

      -        (b )      -        (b ) 

Genco(a)

      (b )      8        2        16   

AERG(a)

      (b )      2        (b )      4   

 

(a) Includes allowances consumed that were recorded through purchase accounting.
(b) Less than $1 million.
Schedule Of Excise Taxes
      Three Months      Nine Months  
      2011      2010      2011      2010  

Ameren Missouri

    $ 47       $ 45       $ 110       $ 103   

Ameren Illinois

      10         9         42         41   

Ameren

    $ 57       $ 54       $ 152       $ 144   
Schedule Of Asset Retirement Obligations
      Ameren(a)(b)     Ameren Missouri(b)     Ameren Illinois(c)     Genco     AERG  

Balance at December 31, 2010

    $ 475      $ 363      $ 3      $ 74      $ 35   

Liabilities incurred

      (d )      -        -        (d )      -   

Liabilities settled

      (2 )      (1 )      (d )      (1 )      (d ) 

Accretion in 2011(e)

      21        16        (d )      4        1   

Change in estimates(f)

      (49 )      (44 )      (d )      (2 )      (3 ) 

Balance at September 30, 2011

    $ 445 (g)    $ 334      $ 3      $ 75 (g)    $ 33   

 

(a) Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b) The nuclear decommissioning trust fund assets of $330 million and $337 million as of September 30, 2011, and December 31, 2010, respectively, were restricted for decommissioning of the Callaway energy center.
(c) Balance included in "Other deferred credits and liabilities" on the balance sheet.
(d) Less than $1 million.
(e) Accretion expense was recorded as an increase to regulatory assets at Ameren Missouri and Ameren Illinois.
(f) Ameren Missouri changed estimates related to its Callaway energy center decommissioning costs because of a cost study performed in 2011 and a decline in the cost escalation factor assumptions. Ameren Missouri and Genco changed estimates related to retirement costs for asbestos removal and river structures. Additionally, Genco and AERG changed estimates related to retirement costs for their coal combustion byproduct storage areas.
(g) Balance included $6 million in "Other current liabilities" on the balance sheet as of September 30, 2011.
Equity Changes Attributable To Noncontrolling Interest
      Three Months     Nine Months  
      2011     2010     2011     2010  

Ameren:

         

Noncontrolling interest, beginning of period

    $ 155      $ 206      $ 154      $ 204   

Net income attributable to noncontrolling interest

      2        3        6        10   

Dividends paid to noncontrolling interest holders

      (2 )      (2 )      (5 )      (7 ) 

Purchase of subsidiary preferred shares from noncontrolling interests(a)

      -        (52 )      -        (52 ) 

Noncontrolling interest, end of period

    $ 155      $ 155      $ 155      $ 155   

Genco:

         

Noncontrolling interest, beginning of period

    $ 12      $ 11      $ 11      $ 9   

Net income attributable to noncontrolling interest

      1        1        2        3   

Noncontrolling interest, end of period

    $ 13      $ 12      $ 13      $ 12   

 

(a) Represents preferred stock redemptions of $33 million and $19 million by Ameren Missouri and CILCO, respectively.