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Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Alliant Energy [Member]
Compensation expense	$ 2.1	$ 2.6	$ 3.7	$ 4.8
Income tax benefits	0.9	1.0	1.5	1.9
IPL [Member]
Compensation expense	1.1	1.4	1.9	2.6
Income tax benefits	0.5	0.5	0.8	1.0
WPL [Member]
Compensation expense	0.9	1.0	1.6	1.9
Income tax benefits	$ 0.3	$ 0.4	$ 0.6	$ 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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