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Benefit Plans (Allocation Of Plan Assets) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Equity Securities [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Pension contributions $ 100
Defined Benefit Pension Plans [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Fixed income securities, Target Range Allocation, Minimum 20.00%
Fixed income securities, Target Range Allocation, Maximum 40.00%
Fixed income securities, Actual Allocation 32.00%
Defined Benefit Pension Plans [Member] | Cash And Equivalents [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Cash and equivalents, Target Range Allocation, Minimum 0.00% [1]
Cash and equivalents, Target Range Allocation, Maximum 5.00%
Cash and equivalents, Actual Allocation 13.00% [1]
Defined Benefit Pension Plans [Member] | U.S. Large Cap Core [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 10.00%
Equity securities, Target Range Allocation, Maximum 20.00%
Equity securities, Actual Allocation 12.00%
Defined Benefit Pension Plans [Member] | U.S. Large Cap Value [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 8.00%
Equity securities, Target Range Allocation, Maximum 16.00%
Equity securities, Actual Allocation 10.00%
Defined Benefit Pension Plans [Member] | U.S. Large Cap Growth [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 8.00%
Equity securities, Target Range Allocation, Maximum 16.00%
Equity securities, Actual Allocation 10.00%
Defined Benefit Pension Plans [Member] | U.S. Small Cap Value [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 0.00%
Equity securities, Target Range Allocation, Maximum 6.00%
Equity securities, Actual Allocation 3.00%
Defined Benefit Pension Plans [Member] | U.S. Small Cap Growth [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 0.00%
Equity securities, Target Range Allocation, Maximum 4.00%
Equity securities, Actual Allocation 2.00%
Defined Benefit Pension Plans [Member] | International-Developed Markets [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 12.00%
Equity securities, Target Range Allocation, Maximum 24.00%
Equity securities, Actual Allocation 14.00%
Defined Benefit Pension Plans [Member] | International-Emerging Markets [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Target Range Allocation, Minimum 0.00%
Equity securities, Target Range Allocation, Maximum 8.00%
Equity securities, Actual Allocation 4.00%
Other Postretirement Benefits Plans [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Actual Allocation 58.00%
Fixed income securities, Actual Allocation 31.00%
Other Postretirement Benefits Plans [Member] | IPL [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Actual Allocation 63.00%
Fixed income securities, Actual Allocation 34.00%
Other Postretirement Benefits Plans [Member] | WPL [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Equity securities, Actual Allocation 39.00%
Fixed income securities, Actual Allocation 19.00%
Other Postretirement Benefits Plans [Member] | Cash And Equivalents [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Cash and equivalents, Actual Allocation 11.00%
Other Postretirement Benefits Plans [Member] | Cash And Equivalents [Member] | IPL [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Cash and equivalents, Actual Allocation 3.00%
Other Postretirement Benefits Plans [Member] | Cash And Equivalents [Member] | WPL [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Cash and equivalents, Actual Allocation 42.00%
[1] Pension contributions of $100 million were made in late December 2011 and were invested in equity futures.