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Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Alliant Energy [Member]
Compensation expense	$ 0.1	$ 0.1	$ 3.8	$ 4.9
Income tax benefits	0	0.1	1.5	2.0
IPL [Member]
Compensation expense	0.1	0.1	2.0	2.7
Income tax benefits	0	0.1	0.8	1.1
WPL [Member]
Compensation expense	0.1	0.1	1.7	2.0
Income tax benefits	$ 0.1	$ 0	$ 0.7	$ 0.8

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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