Benefit Plans (Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
401(k) costs	$ 6.4	$ 5.3	$ 18.7	$ 17.3
IPL [Member]
401(k) costs	3.3	2.7	9.6	8.4
WPL [Member]
401(k) costs	$ 2.9	$ 2.4	$ 8.4	$ 8.3