Benefit Plans (Defined Contribution Retirement Plans) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
401(k) costs	$ 6.7		$ 5.9
IPL [Member]
401(k) costs	3.4	[1]	3.1	[1]
WPL [Member]
401(k) costs	$ 2.9	[1]	$ 2.6	[1]

[1] IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.