Discontinued Operations and Assets and Liabilities Held For Sale (Components Of Assets And Liabilities Held For Sale In Consolidated Balance Sheets) (Details) - Alliant Energy and IPL [Member] - Gas Distribution [Member] $ in Millions	Dec. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Current assets	$ 1.1
Property, plant and equipment, net	11.0
Non-current regulatory assets	7.0
Total assets held for sale	19.1
Current liabilities	1.0
Other liabilities	7.1
Total liabilities held for sale	8.1
Net assets held for sale	$ 11.0