Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation expense	$ 18.0	$ 10.7	$ 15.3
Income tax benefits	7.4	4.4	6.2
IPL [Member]
Compensation expense	9.5	5.7	8.3
Income tax benefits	4.0	2.4	3.4
WPL [Member]
Compensation expense	7.9	4.7	6.4
Income tax benefits	$ 3.2	$ 1.9	$ 2.6