Benefit Plans (Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
401(k) costs	$ 5.6	$ 6.4	$ 17.5	$ 18.7
IPL [Member]
401(k) costs	2.8	3.3	8.8	9.6
WPL [Member]
401(k) costs	$ 2.6	$ 2.9	$ 8.0	$ 8.4