Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current environmental liabilities	$ 3.7	$ 4.8
Non-current environmental liabilities	25.3	28.8
Total environmental liabilities	29.0	33.6
IPL [Member]
Current environmental liabilities	2.5	3.5
Non-current environmental liabilities	23.2	24.9
Total environmental liabilities	25.7	28.4
WPL [Member]
Current environmental liabilities	1.2	1.3
Non-current environmental liabilities	2.1	3.8
Total environmental liabilities	$ 3.3	$ 5.1