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Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Compensation expense	$ 2.7	$ 1.6
Income tax benefits	1.1	0.6
IPL [Member]
Compensation expense	1.4	0.8
Income tax benefits	0.6	0.3
WPL [Member]
Compensation expense	1.1	0.7
Income tax benefits	$ 0.5	$ 0.3

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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