v2.4.0.6
Summary Of Significant Accounting Policies (Schedule Of Electric Plant In Service) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service, total $ 9,070.7 $ 8,165.4
Generation [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 4,798.9 4,100.6
Distribution [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 3,981.5 3,782.1
Other [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 290.3 282.7
IPL [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service, total 4,815.2 4,684.0
IPL [Member] | Generation [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 2,393.0 2,392.3
IPL [Member] | Distribution [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 2,205.9 2,074.8
IPL [Member] | Other [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 216.3 216.9
WPL [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service, total 4,255.5 3,481.4
WPL [Member] | Generation [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 2,405.9 1,708.3
WPL [Member] | Distribution [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service 1,775.6 1,707.3
WPL [Member] | Other [Member]
    
Public Utility, Property, Plant and Equipment [Line Items]    
Electric utilities, plant in service $ 74.0 $ 65.8