Benefit Plans (Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
401(k) costs	$ 6.2	$ 6.7
IPL [Member]
401(k) costs	3.1	3.4
WPL [Member]
401(k) costs	$ 2.8	$ 2.9