Utility Rate Cases	3 Months Ended
Utility Rate Cases	Mar. 31, 2012
Utility Rate Cases	(2) UTILITY RATE CASES WPL's Retail Fuel-related Rate Case (2012 Test Year)—In December 2011, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $4 million related to expected changes in retail electric production fuel and energy purchases costs (fuel-related costs). The December 2011 order also required WPL to defer direct Cross-State Air Pollution Rule (CSAPR) compliance costs that are not included in the fuel monitoring level and set a zero percent tolerance band for the CSAPR-related deferral. The 2012 fuel-related costs, excluding deferred CSAPR compliance costs, will be monitored using an annual bandwidth of plus or minus 2%. The rate change granted from this request was effective Jan. 1, 2012. Subsequent to the PSCW order issued in December 2011, the U.S. Court of Appeals for the D.C. Circuit stayed the implementation of CSAPR and as a result, the Clean Air Interstate Rule (CAIR) remains effective. Alliant Energy and WPL are currently unable to predict the final outcome of the CSAPR stay and its impact on their financial condition or results of operations.
IPL [Member]
Utility Rate Cases	(2) UTILITY RATE CASES WPL's Retail Fuel-related Rate Case (2012 Test Year)—In December 2011, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $4 million related to expected changes in retail electric production fuel and energy purchases costs (fuel-related costs). The December 2011 order also required WPL to defer direct Cross-State Air Pollution Rule (CSAPR) compliance costs that are not included in the fuel monitoring level and set a zero percent tolerance band for the CSAPR-related deferral. The 2012 fuel-related costs, excluding deferred CSAPR compliance costs, will be monitored using an annual bandwidth of plus or minus 2%. The rate change granted from this request was effective Jan. 1, 2012. Subsequent to the PSCW order issued in December 2011, the U.S. Court of Appeals for the D.C. Circuit stayed the implementation of CSAPR and as a result, the Clean Air Interstate Rule (CAIR) remains effective. Alliant Energy and WPL are currently unable to predict the final outcome of the CSAPR stay and its impact on their financial condition or results of operations.
WPL [Member]
Utility Rate Cases	(2) UTILITY RATE CASES WPL's Retail Fuel-related Rate Case (2012 Test Year)—In December 2011, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $4 million related to expected changes in retail electric production fuel and energy purchases costs (fuel-related costs). The December 2011 order also required WPL to defer direct Cross-State Air Pollution Rule (CSAPR) compliance costs that are not included in the fuel monitoring level and set a zero percent tolerance band for the CSAPR-related deferral. The 2012 fuel-related costs, excluding deferred CSAPR compliance costs, will be monitored using an annual bandwidth of plus or minus 2%. The rate change granted from this request was effective Jan. 1, 2012. Subsequent to the PSCW order issued in December 2011, the U.S. Court of Appeals for the D.C. Circuit stayed the implementation of CSAPR and as a result, the Clean Air Interstate Rule (CAIR) remains effective. Alliant Energy and WPL are currently unable to predict the final outcome of the CSAPR stay and its impact on their financial condition or results of operations.