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Debt (Schedule Of Debt-To-Capital Ratios) (Details)
Dec. 31, 2011
Alliant Energy Corporation [Member]
 
Status at Dec. 31, 2011 46.00%
IPL [Member]
 
Status at Dec. 31, 2011 46.00%
WPL [Member]
 
Status at Dec. 31, 2011 45.00%
Maximum [Member] | Alliant Energy Corporation [Member]
 
Requirement 65.00%
Maximum [Member] | IPL [Member]
 
Requirement 58.00%
Maximum [Member] | WPL [Member]
 
Requirement 58.00%