Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
401(k) costs	$ 24.8	$ 23.6	$ 24.9
IPL [Member]
401(k) costs	12.8	12.0	12.7
WPL [Member]
401(k) costs	$ 11.1	$ 10.7	$ 11.2