Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
401(k) costs	$ 5.4		$ 5.2
IPL [Member]
401(k) costs	2.8	[1]	2.7	[1]
WPL [Member]
401(k) costs	$ 2.3	[1]	$ 2.3	[1]

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