Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation expense	$ 15.1	$ 18.0	$ 10.7
Income tax benefits	6.2	7.4	4.4
IPL [Member]
Compensation expense	8.3	9.5	5.7
Income tax benefits	3.4	4.0	2.4
WPL [Member]
Compensation expense	6.4	7.9	4.7
Income tax benefits	$ 2.6	$ 3.2	$ 1.9