Related Parties (Narrative) (Details) (USD $) In Millions, unless otherwise specified			12 Months Ended				12 Months Ended			12 Months Ended
	Dec. 31, 2011 WPL owed ATC [Member]	Dec. 31, 2010 WPL owed ATC [Member]	Dec. 31, 2011 IPL [Member]	Dec. 31, 2010 IPL [Member]	Dec. 31, 2011 WPL [Member]	Dec. 31, 2010 WPL [Member]	Dec. 31, 2011 Franklin County Wind Project [Member] IPL [Member]	Dec. 31, 2011 IPL's Whispering Willow-East Wind Project [Member] IPL Owed RMT [Member]	Dec. 31, 2010 IPL's Whispering Willow-East Wind Project [Member] IPL Owed RMT [Member]	Dec. 31, 2009 IPL's Whispering Willow-East Wind Project [Member] RMT [Member]	Dec. 31, 2011 Neenah Energy Facility [Member] WPL [Member] mW	Dec. 31, 2009 Neenah Energy Facility [Member] WPL [Member]	Dec. 31, 2009 Neenah Energy Facility [Member] Property, Plant And Equipment [Member] WPL [Member]	Dec. 31, 2009 Neenah Energy Facility [Member] Production Fuel [Member] WPL [Member]	Dec. 31, 2009 Neenah Energy Facility [Member] Materials And Supplies [Member] WPL [Member]
Related Party Transaction [Line Items]
Net Amounts Owed	$ 6.0	$ 7.0	$ 82.0	$ 79.0	$ 48.0	$ 42.0		$ 0	$ 0
Proceeds from sale of wind project assets to affiliate			115.3				115.3
Revenue from related parties										45
Electricity acquired											300
Acquired entity, purchase price												$ 92.4	$ 90.0	$ 1.0	$ 1.0