Benefit Plans (Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
401(k) costs	$ 5.7	$ 5.6	$ 11.9	$ 12.3
IPL [Member]
401(k) costs	2.9	2.9	6.0	6.3
WPL [Member]
401(k) costs	$ 2.6	$ 2.6	$ 5.4	$ 5.5